Can't help you with the Up Cancel (I can barely do it myself), and as for hitbox information I would suggest going here:
It has hitbox information for a lot of characters.. including Doc!
As for stages, I tend to like Yoshi's and FoD, but only for certain matchups. For Yoshi's, the low sides and ceiling allow for some low % KO's and if you are good in platforms you can mix a lot up on that stage with wavelands and Bairs.
For FoD, this stage is fine IMO, maybe not as good as Yoshis, but it's great against Falcon (he needs space to move) and any other character that relies heavily on Short hops (Fox, Falco... although Falco can combo the BALLS out of you on this stage, be warned).
In the end it's all about what you are comfortable with. Doc is a character who really isn't affected by what stage he's on too much (unless you want to CG free on FD), more so what stage is bad for your opponent.