What would be some of the main differences I would see in moving from Maine to Northern Virginia?

Other than the difference in diversity, one of the biggest differences for you will be the traffic and the aggressiveness of the drivers in the area. This area has some of the rudest, risk-taking drivers of anywhere in the US. Additionally, Fairfax Co. is one of the wealthiest counties in the US so your cost of living will be much more than you are probably accustomed to. As your comment about independent cities (you didn't say which town you were moving to), many are unincorporated population centers with no mayor or town council and run by the local homeowner's associations. Most of these towns (not cities) are close together so your population listing has no real value. The boundaries of each town can be determined by a traffic light or road intersection.