Minor Alterations and One Possible Major Obstacle
Welcome aboard the RoadTrip America forum.
You'll need to change the order in which you see a few things. For example, Gettysburg should really fall between Philadelphia and Baltimore. Then if you'll be returning to the UK from Miami, your southeastern itinerary makes sense, but if you're returning from Boston, then from Roswell, it should probably go more like Roswell, San Antonio, Houston, Dallas, Memphis, Nashville, New Orleans, Tallahassee, Atlanta, Lynchburg, Boston. Three months leaves you ample time to see as much of America as you like, but I'm curious. Your itinerary seems to be heavily invested in cities. Is there a reason you've listed almost no National Parks or scenic venues? What is the purpose or reason behind the trip? Finally, you haven't addressed what may be your biggest problem. the difficulties and/or high cost that you'll encounter in trying to hire a car since you are all younger than 25? Have you looked into how you'll handle this?
AZBuck