Boating in the Hilton Head/Savannah/ Richmond Hill areas is of course all salt water, and each area has its own sand bar locations (Savannah - inside north tip Wassaw and inside south tip Little Tybee, Richmond Hill - St. Catherine's, Hilton Head - I do not know, but I am sure they have one or more). Most people do water sports in the wide areas of the ICW; the water is more protected from wind and etc. Additionally, there are many places you can anchor off a small beach away from everyone else, but these beaches tend to be small and consist on shells and rocks.
Savannah has a couple of restaurants accessible by water - Crab Shack (only during high tide), AJ's Dockside (has its own deep water dock, but temp. closed to boat traffic due to COVID) and there are a couple of places within walking distance of the marinas in Thunderbolt (small fee to dock). Downtown/Historic Savannah is difficult as the city has never repaired the public dock after Hurricane Matthew. You might be able to dock at the Westin Hotel for a fee(?), and then take the free water taxi to the other side. Hilton Head has several places, and Richmond Hill has one at the marina.
Good lakes are 2-3 hours away.
If you are serious, you should check of availability of rack space at the various marinas, or your ability to keep your boat at your house (HOA rules). I am at Landings Marina, and it is full and only open to The Landings residents. FWIW, I pay $270 per month - the marina is fully staffed and equipped (store/ice/bait/drinks/snacks, fuel, 15+ wash racks, 2 negative forklifts to work 2 launch/retrieve docks).
