2 areas that haven't been mention that are worthwhile IMO is Charleston SC and Savanah Ga. One of our favorite shores to visit lies almost between both cities (guessing around 90 minutes north of Savanah and around 60 minutes south of Charleston).
Mount Pleasant (across Charleston on the bay) has Patriots point which for some reason never grows old with me (tour the carrier Yorktown).
Charleston seems to have easier parking access than Savanah. When in Savanah, we just pay for the sightseeing trolly tour. Easy access to parking (included in the tour as you're right at the trolley company) and you take the trolleys all day which gives you some amazing information you'd probably never know if you're on your own, added you have a taxi service with the trolley all day to get around the city.
AMAZING history between both cities.
5 - 7 days is what we use to take as a family for visiting, ample time.
Honestly, not certain if July would be a good month though. We're a 3.5 hour drive south to Charleston, and I do work in Columbia SC from time to time, and although it gets hot in our area in NC during summer, Columbia (guessing about 2 hours NW of Charleston) always seems 5-10 degrees hotter than our area in NC (that said, we're up towards the Virginia border at a higher elevation, so we always seem cooler in the summer months than the flat laying Raliegh area).
My father always like golfing trips to Myrtle beach SC in the fall, but I don't golf anymore, and I have an office I spend from time to time in Myrtle. Honestly can't stand the place myself as it reminds me of an over-commercialized "tourist trap New Jersey area" where college kids go to get drunk.