compositing is more along the lines of what you would do in After Effects or Shake or the likes. You can have lots of image layers-though defining what you mean by layers might be in order.
In Pro: Windows> Network is a main feature that I miss (knowing about it, anyway). That's not in regular ol' animate. I'd hardly consider any of the assorted versions crippled. Look at the spec sheet for pro, its feature list says more specifically what's 'added' to the basic Animate package.-and you should be able to figure out whether you need that stuff or not. Keep in mind that Toon Boom only sells animation software. Smith Micro sells all sorts of unrelated things. It's a different mind set.
If you were doing all your drawing on paper and scanning, Pro would be vastly superior (you can scan and vectorize in Animate and Studio, but not all within the same piece of software-or level of control that Pro offers).
Nicer brushes (natural media) in pro. Blurs in Pro are more flexible. Though brushes and blurs in Animate are very functional.
Cost thing: You can buy Animate, then upgrade to pro for less than the cost of buying pro in the first place. You could also go from studio to animate to pro for less than the initial cost. (today's pricing, it saves you $700 US over just buying it outright).
Since you mentioned drawing in Photoshop, have you considered TV Paint?
http://www.tvpaint.com It's frame by frame, and bitmapped as well. Also has a 'devoted' following. Their upgrade policy isn't great though (half price, basically-full price if you' re more than a version out of date).