Excellent project Bell!
I bought 4 Oscars in December, and they have grown to the point where I have exactly the same problem as you do, not only with territorial fights, but also with maintaining water purity. Am busy renovating my house at present, and part of this project involves constructing a new playpen for the Oscars.
I can't quite go as big a you are planning, but got "permission" for a 600 gal (2 cubic meters) in the living room. Mine will be all glass, with a filtration dam set up outside the house, connected to a 1000gal rainwater catchment tank, which will be dedicated to the fistank, and provide for regular automated waterchanges.
It'll be good to learn from your experience though, so please keep this thread alive with updates!
Also, for more on tankbuilding, you could do worse than vist
www.plantedtank.net. Not exactly the place for Oscars, but home to a couple of keen DIYers with lots of construction info.
Cheers!
Willem