sgs

I run two 3kw oil heaters on our system often in mid winter - albeit at the 1kW setting.  This is off a 5kW Deye.  They cycle on/off during the day when working from home to keep the two rooms occupied liveable.  They do chow power - but they are probably the simplest form of load for an inverter - a constant resistive load.  There is nothing that makes them "incompatible" with a solar system.
The reason installers say you cannot run them is because they assume people are going to flatten their batteries too quickly and run them into the groud (underspecced system) and then complain - especially during load shedding when there is no grid available.  If you understand how much power your heaters consume, and manage your battery levels accordingly, there should be no issue running them within reason - as already said by others.
I just wanted to add that, assuming you're not off-grid, and there is no loadshedding, you can draw +-15kW from two Deye's in Parallel - as long as the grid is available.  It will "pass through" the excess that is over the 10kW inverter capacity from grid instead and won't trip.  So your chances of tripping anything is very minor!  (In addition, if items such as your geyser is connected as non-essential equipment, their usage won't 'count' towards the inverter's trip limit either - they will just draw any excess that the inverter cannot provide from the grid directly.)
 

I run two 3kw oil heaters on our system often in mid winter - albeit at the 1kW setting.  This is off a 5kW Deye.  They cycle on/off during the day when working from home to keep the two rooms occupied liveable.  They do chow power - but they are probably the simplest form of load for an inverter - a constant resistive load.  There is nothing that makes them "incompatible" with a solar system.
The reason installers say you cannot run them is because they assume people are going to flatten their batteries too quickly and run them into the groud (underspecced system) and then complain - especially during load shedding when there is no grid available.  If you understand how much power your heaters consume, and manage your battery levels accordingly, there should be no issue running them within reason - as already said by others.
I just wanted to add that, assuming you're not off-grid, and there is no loadshedding, you can draw +-15kW from two Deye's in Parallel - as long as the grid is available.  It will "pass through" the excess that is over the 10kW inverter capacity from grid instead and won't trip.  So your chances of tripping anything is very minor!  (In addition, if items such as your geyser is connected as non-essential equipment, their usage won't 'count' towards the inverter's trip limit either - they will just draw any excess that the inverter cannot provide from the grid directly.)
 

I understand that they specifically roll out the Sienna Enlight meters to cater for solar installs.  You'll likely find that when your approval is complete, they will require you to replace the existing meter with one.  I don't know if there is a cost, but I would push for that.
The Enlight doesn't care about reverse flow - it simply charges you for everything you feed back.  They claim it doesn't allow feed back, but if you go look at the meter settings, it has no llimits configured to block feedback - you can theoretically push back 63A permanently.  You'll just need to be ready to pay for it .

This is 100% normal for Pylontech afaik.  The cell balancers kick in at around 88-90% and then charging current drops, and the SOC gets stuck for up to an hour or more where it will suddenly jump and be "full".   How long it does this for depends on the charging current and how out of balance the pack is.
Have you not noticed this before?  This is mine.  Has done it from day 1.

This is 100% normal for Pylontech afaik.  The cell balancers kick in at around 88-90% and then charging current drops, and the SOC gets stuck for up to an hour or more where it will suddenly jump and be "full".   How long it does this for depends on the charging current and how out of balance the pack is.
Have you not noticed this before?  This is mine.  Has done it from day 1.

I purchased this a few years back:
https://www.takealot.com/hansgrohe-crometta-85-overhead-shower-1-spray/PLID53022123
It mixes in air with the water to make the streams much more substantial.  It is super comfy on the skin, no needle-like jets, and really uses much less water than my old shower head while feeling much more natural.  If I didn't know it was a water saving head, I would never have geussed.  I can highly recommend it.

1. Correct - there is no other component required as you are reading the modbus registers directly into HA.
2. Correct.
3. The inverters have a 12V output labelled "RDS" (rapid shutdown) which isn't in use in South Africa.  It is powered as long as the inverter is on.  I was contemplating running that through a 5V buck converter for the module.  (At least my Deye has that - not sure about the Sunsynk - might be model specific.)
However, I had more to run off 5V including a couple of fans, so would have exceeded the output limit of this port.  I rather opted for an external USB supply plugged into a socket next to my inverter's DB board.  Less neat, but requires no hacking.

Also look at ZeroTier One.  It integrates straight into HA (there is an add-on) and with the app on your phone, allows access into your HA from anywhere by just throwing a switch in the app.  Super easy to setup.

Grid tied = can feed back and blend power from grid with PV and battery.  These inverters need to be on the COCT's list, and requires a long approval process, engineer's sign-off, possibly 'reverse flow blocking' etc.  Inverters like e.g. Sunsynk fall in this category.
Off-grid = cannot feed back, only consume grid power to charge batteries or drive the load.  e.g. a glorified UPS - it will use either battery and solar to feed the load or grid - but will never "bridge" the loads with the grid input directly, therefore canot feed back.  This inverter does not need to be on COCT's list, and does not need an engineer's sign-off - only a COC from an electrician.  If it is linked to solar panels, it needs to be registered, but not "approved" as such, by submitting a line drawing and COC to the city.  (They claim this is purely so that they don't hassle you if they see you have panels on your roof.)  Typically Axpert type off-grid inverters fall into this category.
I've been through both approval processes with two properties and the off-grid registration was really just a rubber-stamp exercise - as long as your COC is valid and you haven't done something stupid, they will send you an approval letter.

Grid tied = can feed back and blend power from grid with PV and battery.  These inverters need to be on the COCT's list, and requires a long approval process, engineer's sign-off, possibly 'reverse flow blocking' etc.  Inverters like e.g. Sunsynk fall in this category.
Off-grid = cannot feed back, only consume grid power to charge batteries or drive the load.  e.g. a glorified UPS - it will use either battery and solar to feed the load or grid - but will never "bridge" the loads with the grid input directly, therefore canot feed back.  This inverter does not need to be on COCT's list, and does not need an engineer's sign-off - only a COC from an electrician.  If it is linked to solar panels, it needs to be registered, but not "approved" as such, by submitting a line drawing and COC to the city.  (They claim this is purely so that they don't hassle you if they see you have panels on your roof.)  Typically Axpert type off-grid inverters fall into this category.
I've been through both approval processes with two properties and the off-grid registration was really just a rubber-stamp exercise - as long as your COC is valid and you haven't done something stupid, they will send you an approval letter.

Thanks all!  This is great! 
I should therefore be able to confidently go with the 5kW model if I leave ovens, pools and geysers off the essential side, and adjust our usage accoring to time-of-day.  Going to the 5kW vs the 8kW is an extra R10k+ that can go into solar panels or battery storage - awesome!

Thanks all!  This is great! 
I should therefore be able to confidently go with the 5kW model if I leave ovens, pools and geysers off the essential side, and adjust our usage accoring to time-of-day.  Going to the 5kW vs the 8kW is an extra R10k+ that can go into solar panels or battery storage - awesome!