The ramp at West Point is very good. I have been able to safely launch even at the lowest tides. When things get really busy, there is often overflow parking for a fee. There are also other ramps around if it is too busy.
your salt water license will cover you only on the "York River side" of either bridge, not the pamunkey or mattaponi side and up either river - i.e. the bridges are the dividing line in terms of fresh or salt license requirement