I would say that you should return the fish you have now and try to find some mid-sized shoaling fish. Erised has a good idea about the congos (6 would be good, look for 4m/2f) they will stay in the mid water and very active. Corys or Khuli loaches would look good shoaled up on the bottom half of the tank (4 of them, either species) and I would say go for 4 live bearers (platys,fancy guppies, sword tails and mollies would work) of course having 2m/2f of each is a good idea. With them being live bearers, worrying about feeding the others isn't a problem. If you are going with the smaller fish, I would dump the angel and severum also because it will be hard to keep the other fish alive. Smaller fish mean food for the bigger ones. A friend of mine paid the price for getting an angel in a tank with a few couples of smaller fish and by morning they were gone.
Just here to help...........