Looks like a nice project. I have a few suggestions to start out with on this monster, but I am not going to address filtration or aeration because you and your friend seem to have the under control.
I would have the flow go in one direction so it is like a gently flowing river (like where pimas are native to) that never ends. Also, I would utilize as many plants as possible, namely floating plants that will cut down on some of the algae and fliter the light a little so it is more like the amazon river.
As far as stocking, 8-10 pimas along with other large fish (rtc, tsn, rtcxtsn, etc) should be fine. Though more would probably be fine.