Planning a long road trip

I’m thinking about taking a long (~6 months) road trip next year to see all of the National Parks in the lower 48 (excluding a few I’ve already been to). I also want to check off the remaining 12 states that I haven’t been to.

The plan would be to start in FL (~March) where my parents live and end in TN where I live. I would camp while in the parks but probably stay in hotels the rest of the time.

I plan to budget around $25000. I may travel with my sister but don’t know yet.

Are there any free apps to use for planning? I don’t mind paying once my plans are more definite.

What else do I need to prepare for? I guess I just don’t know what I don’t know.