Good approach!I'm one figure per character as well, but for me I go for my favourite version of the character e.g. Captain America Stealth Suit and Spider-Man Tech suit from Homecoming. I don't do any mods though.
My current challenge is to keep it to twenty 1/6 figures as I collect a bunch of other things like vehicles, 1/12 figures, 1/10 figures etc.
I don’t think I would have the restraint to keep my collection down to twenty figures …would require some very tough decisions.