We use to love taking day trips to Helen when we lived in GA fulltime.
We would come in from the southern side via GA 400, through Dawson and Lumpkin county, which will be the fastest and easiest way for you to get back on I-75 heading south through Atlanta.
If we are towing, we come or go to I-75 through Canton, GA heading to Cumming. From I-85, we take GA129 and go right through Gainesville and have no problems driving through the city.
My kids have camped at Unicoi State Park, but that was in a smaller 5er.
We love North GA so much, we bought an RV Lot sight unseen in Blairsville last year. Drive to BVille, we take GA575/515 through Jasper and Ellijay to avoid GA129 north of Helen. Road is Too winding even when we don't tow.