Welcome to Aquarium Advice. There are some incredibly smart people here. It's a great source of information.
In reference to your powerhead question, a rule of thumb that I've run across is that you should 'turn your tank over' 10 times/hour. If you're going for a full blown reef, the turnover rate should probably be even higher.
One suggestion I can make is read, read, research, and read some more.
, The Conscientious Marine Aquarist by Bob Fenner is a good book to get your hands on.