A Champ is quite a basic circuit and should be excellent for a first project. Your biggest risk, I think, is that it'll give you a taste for more and you'll wish you had done something more complicated and "ideal" the first time around - but that's why there are SECOND projects!
You've already found yourself a good place to ask any questions that come up, so you are bound to get a good final result.
Part of the mojo of a small amp like the Champ is pushing components like the output transformer and its small speaker to their limits (and beyond.) I wouldn't say it'd improve matters to operate beefier parts within their spec'ed limits.