Yeah, go in-ceiling if possible. I went on-wall, but I soundproofed my ceiling and didn't want to punch 4 holes in the ceiling (and I would have never found a good spot that didn't hit a ceiling joist or my hat channel).
Tweeter to the inside is the way to go in that case.
Can you put some other speaker up there? Sure. Heck, if space and money was no limit, then put the biggest speaker model up there and match all of the other speakers. Nobody is going to do that with a large tower style speaker. A speaker the size of a center channel just start to look "large" and "bulky" up on your ceiling.
