Both the Brickhill and Federica (probably too much of a schlep, but you have a fast boat) rivers are very scenic and fun to explore. The anchorage off Table Point on the Brickhill was one of our favorites, we'd dawdle there a few days and use the Whaler all day.
There is a whole bunch to keep you occupied at Cumberland, what a great spot. If the weather is good I'd guess that main anchorage will be fairly crowded on a holiday weekend.
"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"