Sharpey, I suggest you click on planning at the top of the page and review the rules there.
Briefly, you need a permit for entry. You will be looking for an Overnight Paddle permit. The permit is specific to both the date you enter and the place you enter - the Entry Point (EP). Permits are limited with each EP have its own quota. You can reserve your own at
rec.gov . You can also have an outfitter acquire it for you.
Do you have a specific date you are locked into or do you have flexibility? There is no sense planning a route from an EP that has no available permits for your date.
You must stay at a designated campsite. They are first-come, first served - not reservable. Travel in the BW involves a lot of variables - weather, speed - paddling and portaging, your interests while there, etc.
Seclusion is more likely the farther you travel from EPs.