You're allowed to use CG for mirroring, no problem.
There's little restriction in webdesign. There's no template that you have to use or anything, instead there are tags that you'll want to put somewhere on page (navigation, add and, of course, comic itself), the rest is all up to your webdesign skills. In fact, if you have background in webdesign, you probably won't have any problems getting your site up on cg. There are a few mandatory elements that some people don't like, though: add at the top of the page and a link to CG.
CG's a good choice for mirroring, free hosting, not hard to get around.