i agree his tank is way overstocked........male convicts only get six inches, females only get four and i've never seen a twelve inch GT(liveaquaria.com says they max out a 8 inches) so i don't agree with that..........
It doesnt stop there. Adult sizes of your fish list are big.
Oscars = 12-14"
GT's = 12"+
Red Devils/Texas = 12"
Bala Shark = 12-14"
Convicts = 8"
Plecos = anywhere from 4" to 24" depending on species
Clown Loaches = 12"+ (though it takes a while)
as you can see, thats a LOT of fish
You've got time.
Though with those Oscars, not much time. lol THey grow about 1" per month. Within 4-6 months they'll be 4-6" bigger.