i like the idea of keeping the tank wider intead of taller. 4 feet is a long way to reach for aquascaping
one last suggestion, instead of 1 "big azz" pump why not 2 "large" pumps. just a little duplication/redundancy, a little backup in case some pump failure occurs.
very nice idea... bring your dreams to life
keep us posted on progress.
I agree with the 2 pump idea. You will have backup if one pump fails. Personally I would do one overflow where the "elbow" of the tank is and another at one end of the tank. I would then do a return from the sump at the other end of the tank and a waterfall at the elbow as well. This would allow for the flow of the tank to be in one general direction like it is in a river, just my 2 cents