I just bought 6 tiger barbs, acclimated them and put them in the tank. Here's a pic:

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What are your water stats? I personally wouldn't do clowns in a 120 tall. They get big and require a lot of length. I wouldn't put clowns in a tank that wasn't at least 6' in length.
6 Bala sharks will be way too much imo, they get pretty big.
You cannot go wrong with Poly's.. though they dont get along too well with plecos, and your other fish may become food.
Possibly 1. I've seen them ge to around 1', so 6 of them would be a lot of space taken up.
Polypterus, there is several species though, Polyterus Delhezi, Polypterus Senegalus (Dinasaur Bichir), and many more. You can find out more about Poly's here; http://www.monsterfishkeepers.com/forums/forumdisplay.php?108-Polypterus