Thank you so much everyone. Apologies it has taken me a few weeks to reply. I wouldn’t have been able to move this little project forward without all your help.
I’ve gone back and forth between the options you shared and ended up purchasing the IoTaWatt kit, 12x 50A AccuCT (5 and 7 circuits), and 2x 100A AccuCT (top and bottom RCDs). I know this will be overkill on some circuits, and a combination of SCT-013-000 and SCT-006 (as recommended by @philrob - thank you) would be more compact, but it just feels simpler in my little head minimising variation and going for maximum accuracy, even if it’s a bit more expensive or bulky.
Thank you @frogmore for explaining the sizing. And thank you @overasy for your advice about measuring top and bottom RCDs. I’ve had more time to think about what you said and can see this makes a lot more sense and it’s what I hope to do.