MorneDJ

After 2 months I started with my installation and will post progress here as I proceed. After reading a few books and websites I actually decided to do everything myself although I will need some-one to assist in lifting the solar panels onto the roof. This a quick post (while I wait for meeting to start) highlighting a few lessons learned to date:
Get more than 3 quotes and buy the components where you can find the cheapest, even if you can buy from 5 different people. I selected to buy the bulk from one supplier thinking that the supplier will assist with a nice design and advice. Wrong. I will not go into that. There are numerous websites and forums that will assist in advice, and with the money you save you can hire a professional for an hour or 5 to assist in sorting out issues you may have. Note: This is just my opinion, as with a difficult installation I have heard that installers came back a few times to fix some issues. I am speaking from the DIY perspective. If you select to redo your own DB, mark all cables clearly, including the neutral cables. When splitting the DB, make sure that the correct neutral wires are also removed from the "non critical part".  Get a larger DB than what you think you may need.  Working on an old, 20+ year old tile roof is a %^&*(%$, especially if the roof was painted a few times in the past. Lifting tiles is not as easy as it appears on the youtube videos where the guys work with new tiles. A wooden mallet and a large piece of rubber will do wonders to loossen a tile but be careful. I only had to loosen 2 tiles and managed to do without the mallet once I managed to lift the first two tiles. Tiles will be broken. I only did a small section (one string) to lay the conduit for the wires, yet found 2 broken tiles when I lift other tiles. I glued them together using epoxy glue and marked them to ensure that I will never again walk on top of them. They were repositioned to be directly underneath the solar panels. The brandering below these two tiles were from two small pieces of wood. Use garden gloves when working with tiles. I had to change my bank card the next day and they could not verify my fingerprint ... This seems logical, but I initially wanted to lay the conduit diagonally along the roof from the area where the panels will be installed to the location where it leads to the MPPTs. A firewall and rafters however blocked me at a few locations. After lifting 30 tiles I realized that there was no way that I will be able to fit trunking diagonally and had to refit all the tiles and went horizontally to the edge of the roof all along the brandering. Yes, my back was killing me sunday evening. Do not expect great work by the previous builder/roofer. I found a section where they used pieces of offcut brandering to install the roof tiles, which broke either while they installed it (and just decided to fit the roof tiles anyway), or it moved sometime when someone added a new light fitting to the room. Two sections were completely broken and were not even supporting the tiles properly. I was just lucky that it carried my weight and that I did not crash through the roof. Unless you are an electrician, or have an electrician friend, install the conduit in sections, add the wire through that section; mark, bend and fit the new section of conduit and extend the wire through the new section before doing the following section. It is difficult to pull 2 strands of 6mm wire through conduit with 2 bends, and impossible if there are more than 3 bends. I had to cut the conduit and had to start from scratch.  

Just a massive shout-out of thanks for @Jaco de Jongh and, I believe, @plonkster for their help. I find that I do not work 100%, as I love watching the sun minimizing my electricity account.

Normally you'd divide the capacity into the nominal voltage. But the 2000Wh model is really 2500Wh, and the 3000 model is really 3500Wh (down to 0% SoC), so the figures are 50Ah for the smaller unit and 75Ah for the larger one. Multiply by number of modules.
This figure isn't super important. The Multi's internal SOC mechanism uses that to calculate when the battery is full, but since you use the SOC from the BMS anyway it is not a trainsmash if you are slightly off. A value that is in the ballpark is perfectly sufficient.
LiFePO4 with OTHER BMS. Last option on the list if I recall. Unless you have Victron batteries, you're not using a VE.Bus BMS (I have one of those). And two-signal is for batteries that only have two relays (one closes when empty, the other when full). The pylontech does have that, but you don't use it, you use the can cable.
Normally the defaults are fine for a 16-series battery, but the Pylontech is a 15-series battery, so these all have to be taken down a bit.
If the battery has been discharged below the cut-off voltage (determined by the dynamic curve, which I will get to next), it goes into sustain mode. In sustain mode it just tries to nurse the battery until solar can pick it up again. It goes back into self-consumption mode once the sustain voltage has been exceeded by a certain margin (which you can also set). So don't set sustain too high. Something like 49V (3.25V per cell) is perfectly fine.
The dynamic cut-off curve is an improvement on how inverters normally do this (which is to have a single low-voltage disconnect). What it does is allow the battery to dip lower at higher power levels. An LFP battery that's below 49V at no load is almost flat, while the same battery at 2C discharge will dip that low even if full. The BMS is in charge in any case and disconnects if you overdo it, so lots of people simply configure the whole cut-off curve between 45V to 48V. You can play with this, but again it is not too serious if you get it wrong. If you get it too high, then the system might go into sustain prematurely (eg it might go into sustain at 30% SoC), then you simply lower the curve a bit. If you get it too low, the BMS will kick out and leave you in the dark.
The default of restarting at 0.6V above sustain is good. Don't mess with it unless you have good reason to.

OK, I got the ET112 working, and I can see the assistant, but it does not allow me to start the assistant, as I have to select a Grid code selection. When I try to select South Africa: NRS 097-2-1:2017 it asks for a password, which I do not have. Anyone have this password ?

So I had an entertaining weekend and only manages to shock me 7 times due to my own stupidity, and I thoroughly tested the Earth-breaker-switch. Took a long time labelling all the cables, and still have no idea to where the one cable feeds power (lights), and then extending some of the very short cables to something that I can work with. Changed the walled-in DB to a surface mounted structure.
I still need to go and buy an additional 10A CB for the bottom (solar) row, that will only service lights and the lounge (TV, PC) for now. 

So I had an entertaining weekend and only manages to shock me 7 times due to my own stupidity, and I thoroughly tested the Earth-breaker-switch. Took a long time labelling all the cables, and still have no idea to where the one cable feeds power (lights), and then extending some of the very short cables to something that I can work with. Changed the walled-in DB to a surface mounted structure.
I still need to go and buy an additional 10A CB for the bottom (solar) row, that will only service lights and the lounge (TV, PC) for now. 

Just my 5c, shop around. No need to buy everything from one supplier. e.g. The Multiplus II 48/3000/35 is now R13,705.47 (VAT Incl) at Current Automation, and R15,295 at Re-Volt. But the Bluesolar 150/45 is 6,118 at Re-Volt and R6,468.75 at CA. Playing around with the prices from different suppliers I can actually save around R6,500 on a R100,000 system. That is significant at the end of the day. 
I initially looked at the "more cost effective" units, but considering that Solar is a long term process, I decided to go for gold once off (fortunately I have roof space so I can go for Polys instead of monos ...). Looking at the efficiency of the units (read less energy wasted as heat), a more expensive system just win in the long run.
However, as a start, to get a cheaper inverter will allow you to dip your toes in the water, a step I should have taken 5 years ago, but I never did as I just did not had the money for the system I wanted. yes, I had the money for a cheaper system, but I wanted the newer, spankier stuff ... So I wasted time and money waiting, not really learning anything. 
It is one thing reading books and websites on solar installation, I think you only really learn once you have a system and start tinkering. And almost everyone I have spoken to mentioned that you will tinker, will upgrade and will play around. And for that your approach is fine. 
For me, I look at other stuff, including economics. Buying a cheaper system now, just to sell the inverter later for a better one is not economically viable. You will lose a few K and the opportunity to learn from only one system. But, I have to admit, a system such as the Victron is significantly more expensive than the Axpert one.
Again, just my 5c (actually 10c since that is the smallest legal tender I think).

All of the above.
First, the Solis is a grid-tied inverter, or a PV-inverter in Victron Parlance. No batteries. The Goodwe is a hybrid (like the Victron inverters). So put the Goodwe on the right next to the Victron (and the Infini!) and the Solis on the left. Different types.
Quality? Yes. I generally rate Goodwe and Victron above Infini, and quality wise Victron is definitely still a tad above Goodwe.
Price, yes. Leaving out the very expensive Infinis (which nobody buys), you can get very cheap Infinis, followed by Goodwe, followed by Victron, roughly in 20% increasing steps. Packaging differs too: Goodwe bundles two MPPTs inside one unit, with Victron you have to buy those separately (unless you go with an EasySolar model).
Flexibility: Victron kicks dust in the eyes of everything else in this department. If you want to do fancy integration and modbus comms and things, there is no equal.
If you're in software and/or you love open source, no equal.
Technology wise, adding to what TTT said above: Victron inverters are rock-solid work horses, and the internal design is old-school (low frequency). Some marketing people will tell you that is a bad thing (cause new is better, right?). Goodwe makes a slightly more "modern" inverter, but on another thread yesterday we were discussing how the Goodwe manual actually tells you not to run certain kinds of loads on the backup side (which included things like washing machines and other things one would DEFINITELY run during load-shedding). The blue inverter doesn't bat an eye with these. In other words, I get the impression the Goodwe inverter is really a grid-tied unit with an emergency-power feature as a nice extra. The Victron inverter is a proper off-grid inverter that can also tie with the grid, is stackable, and can have AC-tied PV on its output (ie you can attach other PV-inverters to the OUTPUT of the Multiplus and have them work when the grid is off, subject to some caveats).

Fortunately, I avoided electrocution last night installing an efergy energy meter on my mains in. Had an enjoyable few minutes when I tripped the power, still do not know the reason, but I may have suffered a short blackout as I can only remember that blue flash. So, I will definitely make use of an installer. 
Anyway, after recuperating from the short power outage, I revelled in the output of the meter, showing me where I am wasting power. The result was a short family information meeting. I decided not to change the typical usage over the next week, and to start making a few changes next week (energy saving, not more exercise of healthy eating ...) 
Seems that my current, typical night-time usage (22:00 - 06:00) is less than 0.5 kW, with the meter showing less than 0.4 kW for most of the night (0.3 kW this morning). Naturally I took the display to bed to the utter dismay of my wife, but I promised her that it would be a one night stand. 
Will keep on logging the data and provide feedback, but it seems that a 3 kW battery backup should be sufficient for the night after some slight changes in power use. The night-time drain can be traced to:
- A water fountain that was running the whole night;
- 2 or 3 refrigerators that were on the night (not sure of the 3rd one in the apartment);
- A small air pump for a fish tank;
- A media PC that I never switch off;
- A plethora of small lights from chargers, multiplugs, TV's and PC monitors on standby;
- And naturally, vampire drawing from the various chargers located through the house. 
(I live in a secure area and do not need lights around the house at night, so those are always switched off)
 
I have no idea what is running at night in the room of the domestic, but management and a few timers can significantly reduce the night-time draw. 
I like the idea of installing the frames for the solar panels in the meantime. That I can do, will measure the pitch of the roof this weekend.