Awww you are going to have sooo much fun!
Everyone here gave great advice already, so I don't have much to had. We had a cat when I was younger that was pregnant when we got her, and she had the babies in our shed, up in the attic part of it.. We weren't sure how she would react to us, so we visited her, and then she moved her babies more near to us..then with her ok we started playing with them.. oh how i love baby kitties! They are soooo adorable.

Now are you sure you're going to just foster, or is Mommy freckles going to be the latest addition to your cat heaven?

Can't wait to see photos of Mom and then the babies when they arrive. I know you'll do great! You're so good with cats, you're going to be just as great with the kittens!