+1 on Le Chuck's comments.
a 19" would be positively huge in a bartop, but in a 4 player monster it'd look like a postage stamp, so it really is all about proportions.
As for the rotation, I'd also agree with Le chuck, but, being a first cab build, I'd also tend to say keep it simple.
I guess my approach there would be to take the measurements and try to design in space for the rotational aspects (heck, you might go so far as to mount the screen on a rotating backplane), but just leave it fixed for now. That won't add hardly any complexity or time to your build, but, if you DO decide to make it autorotating in the future, you'll be REALLY glad to did the base work.