I fostered for years before I was chosen by my cat.
This was with Cats' Protection. The fostering you do depends on your home.
Mine you can't really shut an area off so I only fostered single or pairs of cats and they had the run of the house.
The most difficult part is in summer, becauses you can't let the cats out. If you have a spare room you can shut that cat in that's not so bad.
I only had kittens twice, and one set were quite old more catlette than kitten.
Be prepared for local press photographers taking pictures to get them rehomed. My friend made the front page with one pic.
Cats' protection supply all food, litter, bowls, disinfecting spray etc. You just need to empty the litter tray and feed them as you would your own cat.
I've fostered cats from a few days to almost two years.
Cats protection also send you on training courses, not oftem but often but they are fun as they are full of people who like cats.