Discus tankmates?

Question
Hi,I recently purchased a 55 gallon aquarium. I was wondering if I would be able to keep a discus with other fish (such as tetras), meaning that it would be the only discus in its tank.  Would the discus be happy? Also, the plan was to have 1 discus, 9 neon/cardinal tetras, and 7 hatchet fish, maybe a silver dollar.  Would those all mix? Would the silver dollar not be happy without other silver dollars? Would the aquarium be maxed out?

P.S. I have an aqua-clear 300 gph filter&&am getting another filter

Answer
Discus are schooling fish and need to be in groups of 5+...they each need 15 gallons...this means a 55 gallon cannot be a discus tank...I would replece discus with an angel...and 9 cardinals, 7 hatchet and no silver dollar (dinner plate sized fish needs school and 100+ gallon tank)...