Check this site out. http://handgunlaw.us/documents/USOffLimitsN-W.pdf
SC is a no carry in an establishment where alcohol is served for consumption purposes. This includes restaurants. So if you can buy it and drink it there, don't bring your gun.
Best bet would be contact the Myrtle Beach PD and get the answers right from the horse's mouth on your other questions. My motto is "Never ask for or receive legal advice from an internet forum". No matter how well intentioned the answer is, it could be the wrong.