I suggest low if you are going to use it consistently. I would also build a V shaped bottom to move the dust down so the collection will be more effective. It is tempting to just use raw ply for the collection chamber, but I suggest you consider adding some sort of slick laminate to the interior to increase movement of sawdust toward the collector port. Given your small collector power, I'd stick with the 2.5 inch for now. You can always re-cut the port opening should you buy a larger unit.
You haven't mentioned your table saw. Does it have under the blade collection and collect sawdust inside the base cabinet? If so, you will just move your collector hose to the saw's dust port. The problem with table saws is the amount of sawdust that comes off the blade on top of the saw. If you are ripping, you want to make sure the blade has fairly deep gullets, which will carry the sawdust down. A friend made his own dust collection by adding a 2.5 inch port to the top of the blade guard. The hose goes from there to a spot beside the saw, where the DC unit gets attached. Helped reduce the flying sawdust.
You will also want to have dust collection in the router fence. I think it was Mike who posted a picture of a fence that was actually a long, narrow box, about 4 inches square, with a cutout for the blade in the middle. One end had a 2.5 inch DC port with a hose leading back into the DC chamber. Most commercial fences have a plastic port right behind the opening for the bit. Here's a pix of one.
The more I do, the less I accomplish.