If you like the green terror the best, I think you could keep some other fish with it. The other non-cichlid fish you listed (hujeta, etc) should be no problem with it in the 120. You may even be able to keep some cichlids with it if you choose. I would go for fish that do not look similar to the GT, so won't be seen as a threat. Belly crawler pike comes to mind as a possible choice.
Or if you prefer the firemouths, tank would be a great size for 6-8 firemouths and a school of Mexican dither fish like goodeids or swordtails
Or if you prefer the firemouths, tank would be a great size for 6-8 firemouths and a school of Mexican dither fish like goodeids or swordtails
