Very interesting indeed.
The bad news is that IoTaWatt can’t break down the individual A,B,C phase power. If the three CTs could be mounted on a common feed of those phases, you can do it, but the way the service is setup with the alternating buss, that isn’t possible. Each buss feeds two of the phases.
The good news is that you can measure the total used by each of the RCS1, RCS2 and RCS3 with just two CTs. So as you said previously, you can get total power (RCS1), RCS2, RCS3, and the power to the Z.x1 CTs as RCS1 - RCS2 - RCS3
The solar is single phase so you can measure that with 1 CT.
That uses 7 inputs. You can then measure 7+ additional inputs. A useful strategy might be to use those inputs to measure your largest or most interesting loads, and then subtract their power from their RCS group to get the residual power used by everything else in that group.
I also see that there are two three-phase loads. Those can also be measured with two CTs in the same way the RCS is measured.
Multiple circuits on the same phase can be measured using multiple 50A CTs and a headphone splitter to combine them into one input. The limitation is that the combined inputs cannot exceed 50A.
That’s the best I can do with the current IoTaWatt firmware. I did some poking around and found an instrument that can sort out the phase power using essentially three CTs on the mains. I found a used model for about $5,000. I don’t know how they do it, but it suggests it can be done with three power meters. There is no demand for this within the IoTaWatt community, but if someone points me to a description of the technique used to do this, I will consider adding it to the firmware, if possible.