sump confusion
 

I was lookong for a new sump for my new 110 gal. tank. I was looking at the Aqueon Pro flex #3.( max size 110gal) I would go with the larger but wont fit under my tank. The #3 holds (if i did my math right) 25.8 gal. Will this be enough? also is this a good system? I was going to use a deep sand bed, good size skimmer(any recomendations) and possibly set up a little refugium in side of it also.I know I could go cheaper and build myself one but dont want to bother and i am not that crafty.
thanks for any input
http://www.aqueonproducts.com/products/proflex-sump.htm