well first, i would use acrylic aquariums, you can get 10g sea clear acrylic aquariums from the fish store in seattle for cheap(that is the ONLY thing that store is good for, horrible otherwise). acrylic is so much easier to do plumbing with, and you will save some money making your own overflows and returns from plumbing parts you can find in any home despot or lowe's.
then you could use a glass tank or even a rubbermaid plastic container (heavy duty ones) for a sump as long as you were going to use submersible return pumps. but if you wanted to use a single external pump to return water to the 3 tanks then you would probably be better with an acrylic sump, again, you could just use an acrylic aquarium from the fish store as a sump.
felt filter socks can be good in a sump as long as you are dilligent about cleaning them every couple days, same goes for polyester filter pads and sponges, you dont want the crap they collect hanging around in your system.
skimmers are imo very important on smaller systems, to name a few that would be good for about 40g total;
aqua c urchin pro
asm g2
percision marine es100
via aqua sk200(go figure, it works great)
the new phosban reactor with the twist off lid is great for carbon/rowaphos, which i think is a must have on any system.
submersible return pumps that would be good would be;
dolphin
sedra
mag
newer gen-x pumps(the older ones have issues)
external return pumps;
iwaki, a little more money, but, they last 10 years