you will have to pay sales tax when you register the car in VA at the DMV. theres no way around it, outside of registering it in another state and then moving it down to virginia and keeping out of state plates. As for the tax credit, i have never heard of an upper limit, but don't take that as gospel.
Not an upper earnings limit to the Federal tax credit. Getting the New Jersey benefit is simple. Move to New Jersey. And if you are concerned that you make too much money, maybe you don't need to worry about it anyway. Just kidding. You don't accumulate money by failing to take advantage of every opportunity.