I have done a lot of miles w/ a sled in the snow, and use a piece of paracord about 12' long to pull. Step into it and start pulling, the cord will settle about where your belt is, and any pouch or knife on your belt will keep it in place. The downside is you have to step aside when going downhill so the sled doesn't run over you. Just depends on the terrain though.
If you are going to have lots of downhills, then you may want a more rigid pipe/harness setup. check out skipulk.com or similar for lots of ideas. They sell a lot of the stuff too.
My last trip was icy, with a ledge along one side of the trail, and the trail sloped toward the ledge, and the sled didn't have any steel runners to hold it. That pretty well stank, but we put a line on the back of the sled, so one guy pulled it and the other one kept it from going over the side or running over the puller.
I try to pack a good sized pack in the sled, so if you need to lighten it up or leave it, you can put the pack on. It is also nice when in tricky terrain when the sled starts to pull you around, you can get more weight over your feet and less in the sled to pull you around.
If you keep the sled @ 40lbs or so it isn't hard to pull; in the right snow conditions you can just pull it with a couple fingers. If the snow is near freezing, you might consider bringing a snowboard glide wax with you, as snow balling up under the sled makes for a really hard pull.