All this advise, and not one of these jokers though to ask the dimensions of your tank


A tank with a footprint of 36" x 12" would be fine for a FM pair. A 30" x 12" would be a little cramped, but do-able.
FMs have been bread over and over so many times that most are not of strong gene pool and will likely not get beyond 5", 6" max. You'll need to come up with a pair so buy 5-6 juvies and grow out until a pair forms, then get rid of the others.
My FMs never bothered my plants, you will need to give them a cavelike area where they can move gravel though. Most likely the ghost shrimp will be eaten.
Covicts and FMs are basically the same size fish. IME cons are not plant friendly.
This is untrue, the pics below are of my female. I lost my male a few months back though and the pair can be seen in the folloeing threads
Firemouth Cichlids with Fry
Firemouth vs. Convict...Battle to the Death