Hello and welcome to RTA !

Good luck finding a road trip buddy and hope you have a great trip. One point I thought I would make is that this a minimum of 5 days driving, (all day with only basic stops) 6 days with a detour to Rushmore, so even with 7 days you are not allowing much time for sight seeing. Google maps and the like are good for route planning and distances but way off with timing when real life issues come into play such as a human's need for rest, food, to use a bathroom and have a little exercise to stretch tired limbs, never mind congestion and construction delays.

Your trip can be acheived but would be more fun and relaxing if you had a little more time or lower expectations. Safe travels !!