IMO the shark is probably the only fish on that list that will go with an eel.
Discus don't belong in a 55gal tank, they need more swimming room. Eels don't belong at discus temps, either. Discus aren't community fish- as Az said, only certain other fish can survive at the temps they need to be kept. None of the fish you listed would really be appropriate.
My best advice is to pick the one fish you're most interested in keeping and then design the rest of the tank around that fish. You've got some serious compatability issues with every stocking plant you've listed so far- if you start with just one species and then build the tank around that you'll end up with a much healthier, happier tank in the long run.
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