I think its wonderful for you to consider adopting a handicapped cat. The only experience I've had is meeting a 3-legged cat in a HHP show. From talking to the owner, the cat doesn't know its really missing a limb. Not sure if this one was born that way from the beginning or was an accident; but you never knew it till it stood up.
They learn to balance on 3 legs and can do modified climbing (depending on if its a front or back leg). If front leg they probably can do more climbing then if its a back one. Same for jumping - two back legs work better.
Bet you'd be surprised as to how much they can do on 3 legs
I'd just be sure to keep kitty inside all the time to protect her.