Elro

You could check whether a 24V Victron Multiplus setup would work for you, but in the long run it's a strong consideration to transition to 48V or even HV batteries, if you want to increase the system power.
What exact batteries have you got, and what's the spec for lifespan or number of cycles ? That might also help guide the level of expense to incur now for the 24V path.
Maybe you could look at options for the best use-case, if you would dedicate this 24V / 3.5kW / 20kWh system to a feed a specific 15A sub-circuit in the house, and get a different 48V inverter system to feed the main circuit breaker. Similar to how you have an MPPT dedicated to a geyser. Meaning, maybe use this exclusively for running an aircon, or a pool pump, or get an electric vehicle.

If I may suggest: plan from the start to buy a good quality inverter, and larger than what you think you need. I know, cost always come into the equation, but so does having to upgrade again in a year or two at additional costs.
A solar power system should be designed to provide for your (expanding) needs for at least 10 years, in my opinion. I am fortunate that I was given this advice before I upgraded from my 2.2kW 24V inverter 21 months ago - I had considered a 5kW system to be "more than I needed" at the time, but was convinced to rather upgrade to a 12kW single-phase inverter, with 8kWh PV panels and 20kWh 52V LiFePO4 batteries. I have been practically off-grid for the last 6 months, with the grid feed to the inverter switched off at the DB board. I am able to run my full house, including a 200l geyser and a large oven without any grid input, only switching the grid on on Sundays for a few hours to keep the utility meter "ticking over", and if rain & heavy clouds lasts for more than 48 hours.

I just had to laugh at your description, picturing you slipping down the roof with a very sore backside - apologies for laughing, but you do paint a vivid picture... glad you managed to stop the splat from happening...
Best of luck with the upgrade - just ask on the Forum before you buy, hopefully the combined wisdom on the forum can save you from making another expensive mistake.

My road to the system I have now has a few kinks, son works from home and where we live power outages are a way of life so bought a system to keep him going, 3.5kw inverter/ 6 x 460w panels/ 1 x 100a/h battery, it was just not enough to keep him going overnight, he has a pc that needs a nuclear power station to run. Realised we were actually saving on electricity. First mistake, no stock in SA to add to this battery, sold it for the same price I bought and decided lets get 4 x 200a/h batteries and also install the geyser system and upgrade the solar panels, sold the old ones(6 months old) what a rabbit hole. I was enjoying myself until I slipped on the coated IBR roof and cracked my coccyx on the ridge and in slow motion proceeded to slide down, fortunately thru the tears was able to hook my heels in the gutter to stop from going splatt. Mistake 2 and 3, realised I could not upgrade the 24v 3.5kw inverter to 5kw( maybe you can explain the problem?) and to make things worse my inverter cannot be paralleled with another. The reason I only have 5 of the 6 panels up is there is no stock of the low mounting steel brackets for the steel rails I used. so have made my own now and will install the 6th panel this coming week.

The "spec" label does not tell the full story. Look in the actual specifications sheet for your PV panels (download it from the internet if you do not have it) for something called "Temperature coefficient (VOC) or something in that line. You should see a small % value - something like (0.30%/°C). You must also know the Open Circuit (VOC) voltage (52.27V according to the lable that you provided).
Here's an example of then calculating the maximum number of panels per serial string:
If:
Panel Voc = 52.27 V at STC (i.e. at 25°C) (from your label)
βVoc = −0.30%/°C (assumed)
Lowest expected temperature = −5°C
Then:
Temperature difference = −30°C
Voc increase = 0.3% x 30 = 9%
So the panel Voc could reach approximately:
52.27 × 1.09 = 57.0 V (per panel)
Your inverter states a maximum PV Array open circuit voltage of 500V. So:
Maximum number of solar panels = 500/57.0 = 8.77 panels... so the maximum safe number of panels per string would be 8 (don't round the 8.77 up to 9...)
Please note that this example is based on some assumptions - you must get the accurate figures and do your own calculations!

The "spec" label does not tell the full story. Look in the actual specifications sheet for your PV panels (download it from the internet if you do not have it) for something called "Temperature coefficient (VOC) or something in that line. You should see a small % value - something like (0.30%/°C). You must also know the Open Circuit (VOC) voltage (52.27V according to the lable that you provided).
Here's an example of then calculating the maximum number of panels per serial string:
If:
Panel Voc = 52.27 V at STC (i.e. at 25°C) (from your label)
βVoc = −0.30%/°C (assumed)
Lowest expected temperature = −5°C
Then:
Temperature difference = −30°C
Voc increase = 0.3% x 30 = 9%
So the panel Voc could reach approximately:
52.27 × 1.09 = 57.0 V (per panel)
Your inverter states a maximum PV Array open circuit voltage of 500V. So:
Maximum number of solar panels = 500/57.0 = 8.77 panels... so the maximum safe number of panels per string would be 8 (don't round the 8.77 up to 9...)
Please note that this example is based on some assumptions - you must get the accurate figures and do your own calculations!