PDQ has it right, with a boat your size and a work schedule you are limited as to when and how you will sail the available river area. Saw several boats around National Harbor and the Wilson bridge yesterday so it can be done, just depends on what you want to get out of your time.
The river starts to widen out near Quantico, but you still have quite a bit of power boaters out from Occoquan and Quantico, plus the through traffic. A bit further south the river starts to twist and turn more so that can restrict you some.
Deale opens up a lot more of the bay and even more places to visit, if that is your bag. But you still have to get there by car. Yesterday it was over an hour from Woodbridge to Stafford on I-95...a single pickup truck caught fire.
Northern Neck is not a bad compromise of good sailing and traffic to get there. Plus it is quite inexpensive to slip there.