as far as other equipment goes, answering your question for the powerheads, you want at least 10x turnover rate for your 55gallon tank of internal flow. (not the flow coming from the skimmer and filter)
so for a 55gallon, you should have a minimum of 555 gallons per hour flowing through it.
Internal powerheads don't have any feet of headpressure pushing down on them, therefore you can go by the actual gph at 0 head.
Therefore, a maxijet 1200 pushes about 295gph at 0 head. Two of these powerheads would give you a lot of flow in the tank, however depending on how they are positioned, you may have a few dead spots. Dead spots are places where the flow does not go and detritus accumulates.
Add a smaller powerhead behind the rocks, like a maxijet 900.
Also, you may want to buy an additional maxijet 1200 to mix saltwater with and to do water changes with.
Besides just that equipment, you also need to consider buying a titanium heater, fish net, fish food, shrimp for fish supplement, extra filter cartridges, extra carbon for your emperor carbon insert.
If you don't want to buy a whole bunch of live rock, you should do half live rock, have base rock. This will cut down on a lot of your expense. The live rock in your system will eventually make the base rock into live rock. Meaning, that if you put base rock in your tank, eventually algae, bacteria, tube worms, coralline and a whole slew of microbiological life forms will accumulate on it.
Good luck and take it easy!