You can just throw canister filters on and be done with it. Each canister filters needs 2 holes so your all set up for 3 canister filters. I would run the intakes under the gravel, one to each back corner and one intake in the middle. You can also run the returns under the gravel and end those with Loc-line to adjust the flow after water is in the tank.
or
If your running a sump you can put all the lines on the outside of the tank to keep the "clean look". The two larger holes are the drains, attach strainers right at gravel level of these bulkheads to keep the fish and gravel out. Then from under the tank run your plumbing up the back side of the tank to the water level you want. Almost to the top. Then put a T filling there. This sets the level of the water and prevents syphon. At the horizontal part of the T fitting run the line back down to the sump, the other end of the T fitting just leave open. Basically the water goes in through the strainers at gravel level then rises up the plumbing in the back of the tank and spills over the T fitting and back down all the way to the sump under the tank. Set your sump up the same way everyone else does,bigger is better.
The return from the sump just use a submersible pump in the sump to pump the water back up to the top of the tank and use a spray bar at the top to agitate the surface and return the water to the tank.
The 4 remaining holes put canister filters on. So you will have the best of both worlds and you will not need check valves! No plumbing will be visible and you will have redundancy with three separate systems. All my tanks use this combination of canister filters and wet/dry filters. I'm very happy with the performance and even more happy with the redundancy.