First, I agree - you need a trainer if you want to teach
the horse (unless you are a very good dressage rider and know how to progress) and show and win
Second, being short (if you are talking about the body, not height) in fact is a positive thing.
My qh is long and it's a huge challenge to keep that impulsion. And let me tell you when she rounds and come on bit she looks very nice. I truly think any horse moving round and freely looks gorgeous (look at before and after pics some people (like say Kayty) posted - horse doesn't look nearly the same!).