I'm not sure if I'm adding anything to the excellent advice that you are already receiving by saying this, but:
It sounds like solitude and being alone are a big part of your goal, yet at the same time, you are concerned about your ability and knowledge to spend 5-7 days backpacking through wilderness. One option, something I like to do sometimes, is not be so focused on traveling a long ways everyday. Instead, hike in a good day or two in on an established trail and then head off trail to establish a basecamp, some place where you can be confident of finding your way back to the trail from. As others have noted, you don't have to get far off trail to get some solitude. Then use that camp as a base for dayhiking, peak-bagging, or (a favorite of mine) just sitting in quiet with my thoughts or a good book. Backpacking does not need to be about covering great distance and ambitious goals, though that is fun sometimes.
Also, check out hiking guidebooks. You can get a lot of really good ideas from them, coupled together with a nice topographical trail map. You can talk to a ranger in advance, for planning purposes: they aren't always that helpful because a lot of their orientation is towards trying to keep people from over-doing their adventure and getting hurt or lost, so they might try to dissuade you from getting off trail, but they can let you know about things like which areas are more private, where the water sources are, fire use regulations, current trail conditions etc. Oh, and tell people (friends and rangers) where you'll be going, for safety (not that I generally remember to do so, but it's smarter to).