Hey B.! I had 3 different doctors for my first two children, and I don't think its a big deal at all! The reason we did is because we moved around a short term internship (twice). I say if you aren't happy, go with your gut and make the change. It's an even longer haul if you dread seeing your doctor, for whatever reason.
In my opinion, OB's are for a safe place to go during pregnancy. In all likelyhood, your OB won't deliver you, but an on call doctor (unless you are induced or get lucky). Doctors just come in the end to catch the baby anyway.
Not sure about the money thing, but I would assume they would take their cut for the beginning and refund you the rest? Just call the office and inquire.
You can set up an interview, not a bad idea. You can ask friends (or on here) but it seems everyone has a different opinion about what they like. I love my OB, but recommended him to a friend and she got her feelings hurt when he suggested she had too much ice cream. Maybe not the best thing to say on his part, but I like his easy going personality.
Let me know if you need any other support!
K.