opinions on sump/fuge for small space

So I'm setting up a 70 ish gallon tank that will be 38"w x 24"d x 20" tall and will sit on some existing built in cabinets I have, the cabinet below that is 18"w x 22"d x 28"t(using just one side of the cabinet since tv components are in the other side of the cabinet). I plan on keeping corals of all types and a few fish- my dilemna is I'd like to build a sump/refugium for the tank but with that space I'm not sure where I would put a top off tank - I can go with just a sump but am worried I may regret not having the fuge- Since all of the pre-made fuges are longer than my space I will likely just build one out of acrylic, maybe a 10" wide x 22" L sump/fuge and then an 8" x 22" tank for my auto top off? Just looking for ideas here ;D

 

I've run into space issues underneath as well. I just picked up a 3 gallon plastic sterilite trash can from walmart that will suffice for me, its footprint is something like 10"x6". I have a 90 gal, and it should hold enough ATO water for 3-4 days, enough for my weekend/wednesday maintenence.