I did a 20G long for my sump. You run out of room quick. Goal is to make fuge as big as possible, return as small as possible, and leave enough room for skimmer and heater. Then you have to make sure you have room for drains. I did same config as you plan (sump/return/fuge). I like it. I just added a BRS Phosphate reactor. Fortunatly I had enough room for the pump in the sump. Old picture from when I first installed it. I have changed the drain into sump. I also took out the 1" pipe from the "T" to the drains and replaced it with 2" pipe. Really slowed down the water and reduced the bubbles considerably. PS: An auto top-off is a must. I had to top off twice a day before I installed a JBJ Auto Top-Off. Good luck, and have fun!