I was quite pleased with the casting, and I think Nolan has chosen these two characters because he has a good idea about what to do with them and by that I mean translate them into something that does fit in the universe.
It's going to be very, very hard to top Ledger's Joker because damn he was good. But Hardy IS a great character actor and in that respect he's puuurfect (oh yes I did) for this role. He has the ability to get buff and nasty. Did you ever see that BBC2 London East End gangster drama? He was was proper naaarsty in it.
Hathaway has the ability but more important the gravitas, the presence. I doubt Nolan'll make her into something too crazy though and she'll probably make Pfeiffer look really over the top. I know what you mean by the blankness though - she's all big eyes and smiles all the time. I'll give her a chance though, and I like her look.
b. You don't really know about Bane's character do you? Find out and then rethink it. Hardy is an excellent choice for it.