I don't think the passes are all that steep on the NT (Washington 20), but they are long -- especially from Mazama up to Washington Pass. So the standard prep answers will fit: get in shape, lose weight early, get used to long hours in the saddle, get used to riding with a load, make sure your gear is in good shape.
WA 20 had some very good scenery, and was well worth the trip for us. It was also fairly remote; you're going to have stretches of 50 miles between services, so make sure you have water and food to cover those stretches.
Somebody else will have to answer your PC questions. I was happy I made the trip on the NT, and very glad to stop when we hit Anacortes. Have fun!