I live in Charleston...
The concerts I have been to at the Volvo have always been in seats, they usually have an area down on the floor, maybe that is general seating as the seats aren't permanent.
The only advantages to staying in Mt.P would be the proximity to the beaches (Sullivans Island and Isle of Palms are both nice and close), and its a short drive to Daniel Island where the concert is, and the ease of driving around in general. If you do stay in MT.P I can vouch for Paige's (I dated Paige for a while
, also best shrimp and grits in the area). Also Langdon's is really good if you are looking for something a little more upscale (small place with a fantastic chef). MT.P to me is just another suburb though and doesn't have the historical feel of downtown.
If you are coming to Charleston for the city and history, the Museum Mile area (never heard it called that) is a great area. Lots of great dining and things to see. I personally would not rent a car if I were flying in. Uber and Lyft are both here and all the drives are short if you needed it. If you are in halfway decent shape you should be able to walk almost everywhere. If it gets hot or you get tired hope in a Uber. If you decide to go to the beach its a short 15 min ride over to the ones near MT.P a little longer to get to John's Island area.
As far as restaurants go down town, there is just so many places that are great and pretty unique. Some of my favorites: The Macintosh, Oku(sushi), Basil (Thia), The Ordinary, Halls Chophouse, Tatooed Moose (more funky). If you really want the best food in town though you need to plan ahead and try to get a table at Fig while your in town. It really is a tier above everything else in my opinion.
If you get tired of downtown while your here, I think Sullivan's island is a must see. Its quintessential Charleston. It is that funky mix of beach town and classic southern feel. All the restaurants on the main street are good, the atmosphere is casual but the quality isn't. I end up spending a lot of time their in the summers. Get a Game Changer at Home Team if you go.