awww...i won't start about shelters..but yes i think its better to save a pet from a shelter..way too many in shelters needing good homes..but i guess there's always a chance of something..from breeders or shelters..Bless you for saving one from a shelter..he's getting a fighting chance..
I've never heard of that FIP before..but i havent owned a cat in a long time..my willy didn't like cats.
I'm so sorry to hear this..
Sending prayers for you and milo that he pulls through this..with a speedy recovery..