I recently bought a 1994 Trek 520. I have been posting a bunch of questions so you may recognize it: https://goo.gl/photos/kShPJGkSKmsQDqURA

My next question is what kind of wheels to get to suit it up for touring? I am coming from ultralight backpacking, so it probably won't ever hold more than about 180 pounds fully loaded including me. I plan to get 28 or 32 schwalbe marathon tires or something similar, leaning toward 32s. My goal is to have the wheel/tire as strong light and low-maintenance as possible.

Right now it has a 700c back wheel but no front wheel. There are 7 gears on the back and 2 in front. The back wheel has a shimano parallax hub with a mavic cosmos rim, both pretty old looking.

What matters when I am looking for a wheel-- old or new? How many spokes? What brand?

Thanks for your help!