As long as she is not crossing the breeds that is ok. Some breeders do work with more then one breed. I thought from your typing these were mixed breed cats
I would look for a breeder that spays/neuters before you get the cat, not just a contract that you will get it done. It's much better when everything is already done for you.
It depends on the breeder really. When I was looking for a Maine Coon, some of the breeders I was considering did the spay/neuter early and some had a s/n contract. Some of the breeders did not agree with early spay/neuter, so they did a contract instead. The breeder we ended up getting a kitten from had a contract which says they should be s/n between 7-9 months old...