Pick what you want to see, visit, etc and how much time at each.
Decide how many miles per day both in mileage and time, you want to drive. Also how much time to break camp and set up each day.
There are a lot of things to see and do between Ohio and Yellowstone and or Calif.
If you have not towed much until the trip, be conservative with you daily driving time and distance. There will be travel hiccups due to construction, accidents, etc.
Destination camping reservations fill up early, enroute camping may be easier, there are lot of resources to help, various rv clubs, AAA, state rv quides. Passport America is a 50 percent club, but does have some restrictions but we have found that for weekday overnights they help keep cost down.
Yellowstone will take several days to really see.
All the way to Calif. and back in 3 weeks is a lot and leaves little time to do other than drive.
Half the fun is what you will see and do getting there, or anywhere.
