once you have one pair of firemouths you're not going to want another pair. Go with one pair, you're going to have too many babies to deal with anyways. Like mentioned before cories do good in groups of 5 or more so I suggest getting a few more.
Whhhheeeellllcome!!!! Glad to have you on board!! Tis a great site indeed is it not? Hopefully you'll love it here as much as the rest of us!!
Thorichthys meeki is definately a great CA cichlid!! Probably one of the more common cichlids, yet still one of the more attractive, appealing ones. I'm sure that at one point or another, EVERYONE here has kept a Thorichthys of some sort. Congrats on moving over to the cichlid side of things. Much more interactive and enjoyable!
You should be able to get at least one pair in that tank, although two pairs isn't completely out of the question. The presence of another pair might promote more flaring, interaction, and other interesting behaviors. Be sure to have plenty of open space though, as they appreciate being able to sift through the sand and substrate.
Broken Line tetras, Flame back tetras, emperor tetras, and serpae tetras are some of my fav. tetras to keep with Thorichthys species. They get a little bit larger, are attractive, and very active!!
Cories are probably the best way to go. Active, easy to keep, and full of vigor, you won't be disappointed. The larger the group of them you have, the better too!
also buenos aites tetras get pretty big. firemouths are awesome, i own 2. now that they are finally just becoming adolecents and not babys anymore, they have calmed down and changed a lot their color is much better and they are so cool.