Should work but combining 5 CTs isn’t necessarily the best way to combine. Better to focus on getting multiple conductors into one CT and then combining maybe two or three (say one for the conductors on one phase and another for conductors on another phase). In the first link there is a three way that looks good.
I’m not following you here. You describe two CTs, each with 45A worth of circuits. You could combine those into one input. Both CTs need to be the same, so lets say you use two 50A CTs. You would configure the input as that model 50A CT.
Regarding capacity, I think 50A would work OK. Here’s why:
Add up all the breakers in your panel. Do they exceed the capacity of the mains? That’s the usual case. Most electrical codes say that a circuit should have a normal draw no more than 80% of the capacity of the breaker. So there is a 25% safety margin. When you see a 30A breaker for, say a water-heater, the nameplate should not exceed 24A. Same goes for all those 15A circuits. Usually a 15A is a lighting circuit, and isn’t expected to draw more than 12A, more like a couple of Amps these days with LED lighting. Plug circuits are 20A and not expected to regularly draw more than 16A. A 1,500W hair dryer draws about 12.5A.
So unless you’re Clark Griswold at Christmas, most of those circuits will never see anything close to 15A, and even less likely at the same time.
So in your example, if there is a major appliance in the mix, discount that at it’s nameplate rating, and then use your judgement for the rest. Once you get everything working, you can look at the actual amps and if there’s a high-roller, it can be segregated.