Slightly more info is needed...
How heavily will you be planting this tank? What kind of fish load?
If your tank is heavily planted, with a light-medium fish load, you don't need much biological filtration... your plants will do that for you, as they have lots of surface area for bacterial colonization, and they themselves filter out the water.
The one thing a plant tank needs (well, not really need, but it would benefit the tank) is mechanical filtration. In order for mechanical filtration to be effective, you need a good flow rate. A flow rate of 5-10x will do just fine for a planted tank.
HTH
-Richer