Welcome to the RTA Forum!

It sounds like the trip you're planning might be workable, but let's start with one rule: ignore the times provided by google or any other mapping software. They just don't hold up in the real world, where you need to factor in things like traffic, construction, fuel, food and rest stops. Adding 20% is a good rough estimate, but the bigger thing is, on a trip like this, calculating hours really doesn't matter anyway. You need to think in terms of driving days.

Also remember, that while you're looking at 6100 miles to go from point to point, you'll probably drive closer to 7 or 8 thousand miles once you factor in driving around cities, in parks, and going to any other places you want to explore.

Your idea to drive 400-500 miles a day is sustainable. That would generally be around 8 hours a day on the road, but keep in mind that when you're on the road for 8 hours, that doesn't leave a lot of time for much else, especially when you're setting up and tearing down camp each night.

If I were you, I'd start laying out a rough day by day itinerary. It's not something you need to stick to, but it is something that can get you a good idea of how far you can really go and how much you could really see with the time you've got available. Based on what you've told us so far, you should be able to put together a nice trip, but it's not one where you'll be able to spend much time at any one spot.