How big is the sump? And where are you placing it? <For a gravity drain, it needs to be lower than the tanks ... and the tanks are pretty close to the floor on the pic ... unless your sump is located in a room below.>
how are you hooking up the tanks? Does each tank has an individual return, or are you ganging them up?
I have problem visualizing your setup. Are the last 5 pics that of the sump? or a representative tank?? <if that is a tank, I see potential problems.> Maybe a schematic will help.
If you are ganging the tanks up, they need to be all at the same level, otherwise all the water will drain from the top tanks to the lower tanks. If you are ganging, you need at least 2 drains to the sump, one for each level.
You need some way to control water level inside the tanks, and a way to break siphon in the return in case of power failure. <It appears that your return is above the tank & not in the water - or is that airline nipples? Anyways, an airgap in the return will work as antisiphon device.
If you want to run also a canister as a filter, you would run it in the sump (treat the sump just like an ordinary tank for this hookup) to pick up debris. You cannot have it in line with your system (problem with water head pressure, unbalanced flow causing floods, etc.)
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.