I read your sump thread, and this one. As a freshy and a saltie, I have experience with sumps.
Let me give you some low down on the basics.
A sump is essentially a wet/dry filter. Because you are setting up a freshwater tank, I am going to give you freshwater information, rather than salt, because the setup is slightly different for the two.
For freshwater, a good bet for you would be to buy a premanufactured wet dry filter for your tank. You are already drilled so you will not need an overflow. You will not need any HOB type filter or any other filtration. The sump IS your filter.
I suggest you look into something like this:
http://www.thatpetplace.com/pet/product/productInfo.web?picGroupKey=10627
You will want to keep the bio-bale media in there, and possibly add a layer of filter floss. In the additional "empty" resovoir area, you will put your heater and other equipment (tho I don't know what else you would need for a FW sump setup).
Alternatively and, I encourage you to explore this route, Your setup would be perfect for a canister filter. They are easy to use, maintain and provide probably the best possible filtration for FW tanks. You could connect the plumbing for it directly to your predrilled overflow.
I suggest ehiem or filstar for a canister filter.
Avoid getting an HOB, and biowheels are really just eye candy that cost more money. You would be much wiser to spend on a wet dry or a canister.
Hope this helps