Hey, I did something similar on my 30G. Do you want to have the sump sitting next to the tank, instead of underneath it? I like that better than having the sump underneath the tank. Easy access to the sump, and you get to watch it work.
A regular PVC siphon will keep water flowing from the aquarium to the sump. The kind shaped like an over-turned U, with two little U's at each end (like the stickies). The U's at each end keep the siphon primed with water, even if the water level drops underneath the ends of the siphon -- very handy. The height of the little U inside the aquarium decides the water level where the siphon stops flowing. In your sketch, it's the same shape as the siphon drawn there, but flip your sketched siphon the other way. The little U's on each end need to face UP, and the big U should be going over the edge of the aquarium.
What makes it work is putting the pump in the sump, not in the aquarium, and making the siphon out of the aquarium have a much bigger water flow rate than the sump pump pushing water back into the aquarium. I used 1.25" PVC for the siphon out of the tank, but only 0.75" PVC going back from the sump into the tank.
To stop flooding, you just need to lift the sump high enough so that the water lines between sump and aquarium level themselves out, without one of the water lines having to flood out of its container to get there. The top edge of the sump needs to be nearly the same height, or the same height, as the top edge of the aquarium.
For a stand for the sump on the cheap, just get some concrete cinder blocks from Home Depot or a store like that for $0.80 or $0.90 cents each, make a base for the sump, layer of plywood from the store's scrap wood bin, repeat as needed. It can look pretty nice, if you cover it with a decorative material, or paint, etc. The concrete blocks are just cheap and strong, and easy to find.
Here's a rough sketch showing how the water flows between sump and aquarium . . . hope it helps!
