It sounds like you've allowed for 2-3 days in each city, which will be nice. I live midway between Richmond and Charlottesville, and would be glad to offer some suggestions. In Charlottesville, definitely visit Thomas Jefferson's home, Monticello. Also, James Monroe's home, Ashlawn-Highland is close by. For a nice meal, try Michie Tavern. If you're interested in wines, there are quite a few wineries within 30 miles of Charlottesville. Richmond and Petersburg are great for War Between the States (Civil War) history. The White House of the Confederacy (where Jefferson Davis resided)is located in downtown Richmond, and is a good place to start. Between Richmond and Williamsburg, is Route 5. This road is where quite a few plantations are located. They are open on a daily basis. I recommend Berkeley Plantation, and John Tyler's home. Route 5 is a beautiful way to get to Williamsburg. You may want to allow 3-4 days in Williamsburg. It really is the home of Virginia history. There are so many historic homes, like Carter's Grove, the re-created Williamsburg itself, multiple wineries, and good restaurants.
Finally, as far as beaches go, they will all be quiet after the first weekend in September. I recommend Virginia Beach over the beaches in Norfolk. It is prettier, and cleaner. I wouldn't skip Norfolk---there are some neat tours available of the naval bases, but for the beach itself, go to Va. Beach. Hope this helps.