Here is my current thought about my configuration.
First it is not simple to correctly size an installation but I have a big advantage over you as my installation will be connected to the grid. From what I understand, in theory, the total power that your inverters need to provide correspond to the maximum power of what you can draw at a certain time. However, as I said my installation will be connected to the grid and, in overload situation, the extra power can always come from it. So, my idea at the moment (will see what the architect thinks) is to go with a Muti RS 6000 VA and in parallel a Fronius Primo 3.6. During the day, when the sun provides the power, I can hope for about 8.6 kW and during the night for about 5 kW (6 kVA). So, based on this information I think I will install either 12 or 16 kWc of solar panels. This corresponds to 30 or 40 400 Wc panels. They will be organized in a series of 10 delivering a maximum voltage around 410 V with a current of 12A. One string will be handled by the Multi RS one string by the Fronius and the last two by a Victron MPPT RS 450/100. For the batteries I am thinking of using two sets of 16 EVE 304 AH cells with two JK-BMS 200A (should provide above 30 kW). For monitoring the inverters/charge controllers I will use a Cerbo GX and for monitoring the set of two batteries, I will be using a Victron SmartShunt 500A. The Multi RS and the MPPT RS will be communicating over a VE.Can bus and the SmartShunt over a VE. direct bus. The Cerbo and the Fronius will be connected over ethernet.
As you mentioned currently, there are a lot of limitations in the Multi RS firmware: No support for ESS, no support for parallel/3 phases, and apparently not all the information is returned correctly either through MQQT or Modbus. But apparently, they are working of fixing these problems and by the time I will buy the equipment I hope these problems will be fixed.
Below is a simplified diagram of my current thinking
