Living in the area I can tell you that you've made an excellent choice.
As far as picking a site...you won't find many bad ones at Charleston, it is the best park I've ever camped at including Sandbanks and a dozen others.
As far as the fishing goes, the smallies can be great! and the largies as well but are a bit tougher to find on this deep lake. Big Pike are in there but tougher to find.
The lake is loaded with stocked lakers, and with downriggers can result in a great morning fish everyday.
The beaches are awesome, the water is clean and the fish bite.
Enjoy your vacation.
RJ