There is no reffing limit, no, but do be careful as if you take too many, you may be unable to manage them.
You can do whatever you want with your Pokemon. I have a Snorunt and Pichu who will never evolve.
I'm really not the one who ultimately makes decisions on viable Gyms but it's entirely possible. To me, Desert seems relatively balanced since they all tend to be Ground and there are only a few other 'mon that would fit the bill that aren't.