Like Al said, rack em' up. You can rack up two 40g tanks easily and have plenty of room to view everything. I've put three 55g tanks racked up to the ceiling. I think you can fairly easily rack up four 20g longs...
What I would do in your position is buy three 55g tanks and rack em' to the ceiling. One would be for fish, the next for corals, and the next for saltwater mixing / water changes on the bottom. save a little room doing it that way. rack em' up
put the fish only tank at the top and put some cheap shop light on top of it, in the middle tank you can install some cheap retrofit t5s for your corals and then at the bottom use an external pump to mix your saltwater and pump it directly to your display tank for water changes.
I'de also make one of those closed loops of yours able to attach a vinyl hose or a python hose to it or something so that you can pump water out of your tank for water changes. That's how I did it on my 240 - and it saved my back.