Thanks everyone for the recommendations.
I ended up arriving to downtown Charleston at 4:00 pm Thursday, and I also had most of Friday free for sightseeing (except for a couple of hours for the rehearsal dinner). On Thursday I went to the visitor center and they offered my wife and I free tickets to three attractions if we would sit through 90 minutes of a sales presentation, a time share. We did it even though we didn't have much time, since it would save us $122. And that way we were able to do a carriage tour, a ghost tour and we also got tickets to the Magnolia plantation. It was worth it. I also managed to go to Folly Beach while my wife was at the rehearsal.
I really liked Charleston, it has a rich history and I would love to go back to spend more time there. There are so many museums that I would love to visit. I noticed a lot of streets are called Ashley something...Ashley Ave, Ashley Rd, etc. I dropped my wife at Ashley Avenue near downtown for the rehearsal and I drove to...Ashley Avenue...in Folly Beach.
As far as traffic, it was definitely bad on Friday evening, but it was manageable. We parked at the visitor's center for only $2.00, which was convenient. On Saturday we didn't have problems getting to the wedding (in Ashley Avenue near downtown), so it all worked out great.