Keeping African cichlids with South American cichlids is a bad idea simply because of the extremely different ares they come from - all fish can usually adapt to a different pH, but in this case it might just a bit extreme.
Firemouths can get aggressive and are not the best choice ever.
Other suggestions:
Discuss and Silver dollars grow too big.
Some fish I'd consider interesting - Megaletchys thoracata, Platydoras costatus, plecos (clown plecos rule, imo anyway), maybe some smaller species of spiny eels if you're prepared to target feed frozen bloodworm.
Now for a short rant...
I see people asking for tank suggestions all the time, and that's kinda fine, however not having any idea on what they want is a bit ignorant. All the forum posters have lives (I'm not saying I'm not more than happy to spend time on here) and maybe it would be nice for posters to just once do some research on their own. And that's all kind of ok, untill somebody asks for advice and has new fish 6 hours later before anybody really gets a chance to respond, that's just wrong.