now.. Since I'm already taking the larger tank plunge, and there is the chance that I might want to go bigger if I just go 75.. What say a 125 long? (that way I'm not doing it twice, and ticking off the wife)

I think this is plenty, 6' long by what woul that be, 24x24? or 18x18? something like that. I think this is a better way to go, post pone the tank a couple extra weeks/ months and just go all out. corner over flows? center? whats best in this case or both? this is going to be a super awesome project!