Well ideally you want your sump/refuge to be as large as possible. So I would try to figure out what the largest size is you can get into the stand and then work from there. If your going to do an external pump then it will be good to have your pump selected now so you can use that pumps dimentions as a factor in sizing the sump.
1200GPH is a good starting point for a 110 gal
tank. I would suggest the little giant pumps. I have one thats rated for something like 1300+gph
and i get a good amount of flow out of it for over a year and half with no problems.