We have taken a number of long trips from 1 - 5 months. Our overarching 'rule of thumb', as a starting point, is an average of 100 miles for every day 'out'. So 30 days, we start planning about a 3000 mile trip. We'll have long drive days, followed by a couple days of local sightseeing. This rule leaves plenty of time for meaningful sight seeing, and leaves you feeling a reasonable balance between driving days and touring days. OUr trips often grow into some more miles, but it is a disciplined planned growth still aiming for the drive/see/tour/hike balance. Good luck in your planning.