If I am absolutely honest, I would want a 6 ft tank for green terrors, but would then keep them with other fish too. They do grow up to 12", after all.
A 4 fter like that should be fine for 2 or 4 convicts (do some research on numbers) with some schoolers (larger tetras, medium rasboras/barbs, etc.) and plecos (or maybe even Corys). If it were my tank, I'd stock it with the following:
* 1 pair of blue Acaras (look similar to green terrors, but grow up to 7" instead of 12") - I'd make sure to get a ("proven") pair, or would get 6 juveniles and return 4 when they paired off
* 15+ 3" tetras of one species
* 5 mixed plecos that grow up to 6-8"
That would actually be a pretty neat almost-biotope.