We rode from south to north through SC but did vary from the maps when we came into Charleston to visit family for a few days. And you are right, the roads in SC are as bad as they get. Of the 37 states I have ridden in I must say SC is the worst.
It does sound like you may not have as much experience on busy roads as you will need. Once you get some, you won't feel like you are going to die, but you will be annoyed and angry, and scared at times.
If you want to read the experiences I had riding through the state, and the whole route (as far north as DC) check out my journal on CGOB at www.crazyguyonabike.com/doc/FA2012