Doesn't sound like a good combo to me plus you are going to be overcrowded once these fish grow up. Also you are most likely going to have the same problem if you get the GT, one fish for your 75g. If you want more of a community SA setup I'd stick to more peaceful species. I personally think a school of 6 Geophagus sp. Redhead Tapajos would be a perfect addition plus you can add other community fish. There are a variety of fish that don't get huge and work well in a community setup you just have to do some research and be patient. Good luck!