Stocking 66 Gallon (40 x 20 x 20) tank

Hello, thats my first topic here, to explain in short i were with Discus but my canister give me a problem and they all die from lack of oxygen...
i'm probably never again trusting them to principal filter, i may put him as a help (its a 270GPH, and working, not something that we just throw away, especially because the prices from Brazil...) now im with a sump, with an chinese pump, Resun B-2000 (540GPH) but i probably will use her for salt mixing in a reef project and buy a 660GPH more trustfull pump..

Leaving introductions away, as the title says, now i'm re-stocking the tank, it's a 40 x 20 x 20 tank (i'm Brazillian so a more correct measure would be 100 x 50 x 50cm)
i'm planning on put a single Oscar in there, but many people say the minimum would be 75 gallon so i'm open to sugestion...
i would like american chiclids, if i don't find a nice sotck list i'll go with some schooling fish in great numbers (Cardinal Tetra x 120 or something among those lines) or a schooling communityor even get back with Discus

that's pretty much all i have to ask, Could an Oscar live him all-life in 66 Gal ? if not would you please sugest some stocking ?

So as do i, but i where wanting know more people opnion, i usually found stuff talking of 55 gal, most experienced says 75 another says 90, other says that 55 is fine but should be at least 48", i know, the bigver the better but in Brazil an bigger tank is very expensive..

Aniway next week i guess i will start hunting for an baby albino red tiger at the lfs

Hello, and merry Xmas
i am with the chance of getting a 40 x 20 x 25 tank, the details would be a pain to explain so i'll jump that part;
But it would be some nice 83 gallon (right ?) and i was wondering... Would be OK put a Bichir Senegalus or a Pleco or some other gravel fish ?

If dont i guess i will put a 40 x 20 x 22 or 23 just to make a better tank for the oscar, that all, woul be nice get a quickly a possible answer because i will need to take out the 66 gallon an get the 1 or 2 inch oscar that i'll buy into a 10 or 30 gallon tank (probably 10) so the sooner i get a conclusion the better will be
thanks everyone, later when he/she get over 5 inch i will make a topic for the tank

Here am i just a few minutes after the first post and reach some ideas

first of all, if will be the oscar alone will be a 40 x 20 x 24, some 80 gallon

and second, what you guys think about a Raphael catfish ?