Man, I share the same aspiration as you. When I moved out, I'm gonna build a GIGANTIC tanks for my puffers! It would be like a few years from now, and I think by then you would have your Huge tank up and running (remember to post up your pictures of tank!). You gonna show me some pointers then yea.
I agree with you and your GSP.If I got such a big spare tank at hand, I would probably add in say 2 GSP for that fella. (Increases the chances of breeding). WO, picture these, a huge tank with 3 GSP. No fights, No biting, hopefully breeding in a real cool marine tanks with those blue lights. sweetpie man.
I maintain a few extremely HUGE tank at the local aquarium I intern in. We have to dive in to siphon(VACCUM) out the debris every day. No filtration for these BIGGGG tanks, just WC with new fresh conditioned water 24/7. But I think couple of efficient filtration systems would be neat enough for your project. WC would be like a half day affair. HAHA
But nothing beats happy interactive puffers.