I have fostered a partially blind and deaf cat and a fully blind and deaf cat at the same time - I did keep them in one room while I wasn't around to supervise, although that was mainly cos one of my other fosters wasn't very sociable and would go for most cats, so ones that ignored her especially ignored her. What amazed me was how well they adapted, the partially blind cat could even get up and down the stairs with no problems (and my stairs have no backs, so playful cats have fallen through them!! FIV should be fine as long as you do very graual introductions to make sure there is no aggression. Most rescues do expect you to keep foster cats separate from your own though, so would you have room to separate?