2) Does anyone know what the story is on the contention that Crusade was initially planned to include the original B5 cast?
Well, I don't think it ever was "the original cast of B5". However, I remember there being quotes (including from JMS) back when Crusade was in development about how "some" or "two or three" or something like that B5 characters might end up on Crusade. The quotes also included plenty of qualifiers about how many and which characters depending on several factors or "how things go" or something like that. Presumably, that means that in addition JMS making an artistic writing decision it would also depend studio / network input and, of course, on whether contracts could be worked out with the individual actors and their agents.
I think that it is safe to say that preliminary discussions were held with a few of the original cast about the possibility of being regular, or at least recurring, cast members of Crusade. Those discussions would have been procedding from thumbnail outlines of Crusade that involved some different cast members than we actually saw.
What's up with Claudia and Bruce being pissed of at Joe?
In Claudia's case I think that it arose from some exchanges of quotes when she left, things about whose choice it was that she wasn't returning and whether anyone was purposely lying to the fans. There may have also been a seed of frustration left in Claudia because she felt that she wasn't given much of anything to do in the 4th season, aside from being a news reader as the "Voice of the Resistance".
In Bruce's case, I remember reading the quotes where he expresses some irritation with JMS but I forget the details now. I think that it was centered around the way the Crusade planning / casting / discussions were handled with respect to the end of original series and who was and was not told what, and when; etc., etc. I don't think that it was anything that ever came up when they were actually working together on B5.
If someone has a clearer memory of those events, or the time and motivation to chase down all of the old quotes, please feel free to correct me.