any of the sharks would be great but for a 55 i'd just have one shark and no other bottom feeders like the cories or the kuhli loaches. however you could definitely keep the corycats and the kuhli loaches together without the RTS, in a 55 i'd go with six of each
the pearl gourami and the rams could definitely be kept together, i think the firemouths might be able to be with them too but i'm not sure on that, i remember reading that they were pretty peaceful fish
for your 55 in particular i'd go with....
6 corycats
6 kuhlis
2 rams
1 pearl gourami
6 praecox rainbows (the dwarf neon rainbows)
and maybe some smaller schooling fish such as rummynose tetras or something similar, whatever you like really
