Since no one has addressed this part of your question, I'll help out with it.

Keep your fosters separated from your kitties until the entire series of vaccinations are complete (which at the same time is also a quaranteen (sp?) period in case any kittens are incubating anything)

You don't want to rush getting them aquainted only to find out the kittens had a couple earmites that took several weeks to show itself, or incubating a kitty cold that doesn't show up right away. Whether it's to keep your kittens from passing anything to your cats, or something your cats are spreading but not catching themselves, it's always safer to quaranteen (sp?), do all the vaccinations and worming, THEN gradually work on socializing.

Good luck