So 4 weeks is 28 days.

You can drive coast to coast in 5 days though you will not be able to stop and see things. So you are looking 10 days driving. Now that 28 days becomes 18. You spend a day to reach a destination and a day there you just used up 2 days. So you can use that as an initial guide to see how many destinations you can plan on seeing.

So I suggest that you get google maps or similar locate you destinations and learn the mileage between them. Google will give you a route on the Interstates and off them. So you can compare how much time is used up. So with knowing the drive time and how much time spent sight seeing when you get to a stop. You will be able to work out a route.

Personality traits need to be considered. For some people they see a scenic view they have to stop. The see an attraction. Such as the worlds biggest ball of twine. And, they must stop and have their picture taken. The there are those that operate on the lines of Mussolini in that he made the trains run on time so you will have to run your vacation the same.

Me, 4 weeks, enough money, schedule, what schedule, I don't need no stinkin' schedules. And the only chance you would have of catching me on an interstate is I would running out of time and have to get home.

So what is your objective? Is the sights found on the road more important or the destinations?

The answer will guide you as to whether you would enjoy the US routes or the Interstates. Or do a mix of both.

I like the idea of you taking a different route back then you took west. Also like to retrace the same route back going in the opposite direction.

Which ever way you head your car you will have more fun then your car can carry.