Listen, Savannah is a fantastic city, with a ton of things to see, and some fantastic places to eat. The city is absolutely worth visiting, if you have time to actually explore it.
We strongly recommend against trying to do a "daytrip" to any destination that requires 500 miles of driving, because the payoff just isn't worth it. By the time you've arrived there, you practically have to turn around and go back. Its the same reason we strongly advise against people trying to drive from Las Vegas to the Grand Canyon and back in a day. To me, there is a foolish aspect because you're driving more than 100 miles the wrong way (on a very slow and congested road at that) just so you found a "deal" on a hotel. Simply staying in Charleston, saving you at least 4 hours of backtracking, and around $40 in gas, would make a world of difference.
Have you actually done a lot of 500 mile daytrips? It doesn't seem like you have a very accurate view of how long such drives will take. I mean, a 500 mile drive is 8-9 hours, in good conditions, with little traffic or construction, and if you treat it like a speed run. If you do something as simple as stopping for a sit down lunch at a roadside BBQ stand, your travel times will creep up and your available time at your "destinations" will become even more limited.
Ultimately, it is your trip, and you can do whatever you'd like. Your trip is theoretically possible, but you say you "don't want to be exhausted," and I don't know how you'll fit all of your agenda items in without pushing your own physical limits.