Welcome to the RTA Forum!

I think a big reason you're overwhelmed is because you are trying to cram the entire US into one trip. Even if you do decide you can fit in everything you've already listed into 3 weeks, you're going to be much better off breaking things into pieces.

I assume you are thinking of flying from the west coast back to NY? What about your stops in the Southeast - are you going to drive to them from NY, or are you looking at another flight somewhere?

You've got a lot you want to do, and it might be too much to do in 3 weeks, but the easiest way to figure out is to start by mocking up an itinerary, and get a rough idea of what you would do and how much time you'd have to do it. That should give you a better idea of how you want to go about doing your trip, and if it is too much. Once you've got that down, we can help you decide what will work, what won't, and what you can do in between the stops you've listed.