Wouldn't add other cichlids. Firemouths are very aggressive but they cant fight worth crap. They provoke other fish which only get themselves beat up. In a 37 there isn't much hiding space.
The gallons may seem like a lot but the footprint isn't great. A 40 breeder tank could probably do a Firemouth and a Con. Not Salvini. They are absolutely monstrous... Some members here have bad experiences with Acara and Firemouths, but i think the Blues work ok.
Some of the more rugged larger Tetras might be ok (think Lemon, possibly Serpae, Silvertips are borderline) but dont do Tiger Barbs. Maybe Rosy Barbs. Possibly Giant Danios but the tank is a bit short and they are incredibly active...
I would try about 8 Silvertips. They are fast. Try to get them as adults, which should be at about 2". Firemouths should have a hard time eating them.
Cories might work if you get adult ones of a larger specie. They are tough and they shouldnt really get bullied, although its difficult to tell.
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