We retired to Oriental, NC (20 miles from Beaufort) about a year ago and looked extensively in the Northern Neck of Virginia before making this choice and we used to live in Annapolis, so I think I can answer some of your questions. We have cruised and anchored out in both areas.
1. You can leave your boat in the water as far north as Annapolis (or even further) but you need to use an ice eater. The creeks in Annapolis will freeze 2-6" thick. Less in the Norfolk area and essentially not at all in Oriental/Beaufort- maybe an occaisional skim (hasn't happened so far).
2. Sales tax is about the same (5% I think) and both have personal property tax on boats. If you paid sales tax on your boat in Maine, you won't have to do it again in Va or NC.
3. For sailing from Oriental you have the Neuse which is a big wide river. From Norfolk you have the southern Chesapeake and river tributaries. For cruisng from Norfolk you have Back River, Poquoson River and Mobjack Bay which have dozens of nice anchorages. From Oriental/Beaufort you have rivers and creeks off of the Neuse, Cape Lookout, Bath, Washington. I can't say that one is better than the other for either sailing or cruising.
4. I know that the Northern Neck was significantly more expensive than Oriental- about 15-20% more, probably because of the DC weekenders. Norfolk is probably 10% more.
5. The further south you go, the warmer it gets- duh! Oriental is probably a couple of degrees on average warmer than Norfolk.
6. I think that the quality and pricing of the boat yards are the same.
7. There are no jobs in Oriental. But you didn't ask this question.
Send me a PM for any more specific questions- dmfeelingroovy@gmail.com.
David