Convicts can be pretty aggressive from my experience, and i would be more worried about the tetra than the convicts, but since BA's are larger tetra than some, i really don't know. I would try and find other people who have BA's in community tanks, and see what has worked for them. For the tank you are considering i would say some dwarf cichlids would be very suitable depending on how the BA's are torwards them. Most of them i would imagine could take care of themselves. Incidentally, firemouths are central american cichlids, and are little more aggressive than most of the SA dwarf cichlids in a community setting, although less aggresive than convicts.
Having some fast-growing plants (Hygrophila polysperma, foxtail, bacopa, etc) may also help by providing cover, and giving them something to snack on instead of other fish's fins
Having some fast-growing plants (Hygrophila polysperma, foxtail, bacopa, etc) may also help by providing cover, and giving them something to snack on instead of other fish's fins