Yes, Flitwick is most definitely head of Ravenclaw. I'm prepared to bet that Jo's gonna tell us in book five that he is. After all, she told us who the head of Hufflepuff is in book five.
We-ell... Defense Against the Dark Arts... This is just a made-up name, but it might work: Forticus ....Something... I haven't thought of a last name. I don't want to.
Here's another idea: you could make either one of the Teachers Unknown a relative of Lupin's. Perhaps he could also be one of the reasons Remus was able to come to Hogwarts?
Potions Master name: Uh... **Thinks hard.** To tell you the truth, I don't have any ideas right now. Brain hurts. Too many ammonia fumes.