That setup should do fine to start with. As long as you have the right amount of LR, a full cycle, preferably a refugium, which you could modify the Emperor for that and you probably also need some surface skimming. Depending on the fish load whether you will need a protien skimmer or not. If you are planning to have fish and feeding you will more-than-likely need one. Idealy if the back of the tank could be drilled near the top for a 1" bulkhead to surface skim down to a sump/refugium where you could put a small protien skimmer, heater, auto top-off and return pump, you could have a nice set-up.
Didn't see where you listed the light wattage either. Probably a 2x24wt? If so would be OK for zoas mid to top, but 20" deep is iffy on 2x24wt. Might be OK for low light zoas.