#1: No...I wish there was but these are the small small things that make big difference and annoy the users.
#2: Yes T9 offers way to add words, the T9 menu provides the add word option. Usually holding down the * key brings up the menu. Which phone are you using?
#3: It depends on the phone. I believe I have seen it on some implementations of the T9. I think the Q had it. I know most Smartphones consistently capitalize the Is but can't and don't are bit rare.