There's no one right answer without knowing what's going on with the rest of your plans for the tank, but 3-4 "tank turnovers per hour" is considered adequate for all common filtration methods. This would mean 200-300 gph of actual throughput is all you should really need. It depends heavily on your plumbing and other factors, but in most cases this means a pump rated for 500-600 gph.
In-tank waterflow is usually handled as a seperate concern, FYI.
-Matt