Agree with Wills, from the sound of your set up with bogwood etc you are there already for americans. Malawi require a different set up with more rock, coral sand/gravel, not really suited for the plecs and corys. I would recommend Ellioti, not just because I still have some for sale, but they are gorgous fish, comical and inquisitive any agression I have seen is all bluff, they flare thier gills and look tough but thats about it. I had 10 in the tank when the Geophagus Brazilliensis spawned, had fry swimming around in the tank for 13 days and they just never bothered with them. Ditto wills on the convicts, gorgous as they are they are mean little so and so's. Keyholes are also nice, relatively small too, flag/festivum (can never spell it), unless you want to go even smaller Bolivian rams, german blue rams. List is endless really lol
and answer to the next bit I missed lol. I have a pair of wild caught blue acara in with corys, no bother although I do love the acara they do tend to spend more time towards the bottom of the tank amongst the bogwood and java fern, weather its bacuse they are wild and more shy I dont know as they are the only blue acara I have kept.
Firemouths are nice Ellioti are better lol