Northern Virginia: I am moving 300 miles away at the end of January. I have been at my current job for 31/2 years and am on good terms. It is a very small office, under 15 people. Should I give more than two weeks' notice as a courtesy? It is the middle of the company's slow season, so finding and training a replacement would not be a pressing factor.
If you feel it would be helpful, give up to a month's notice. Any longer and your presence will become as wanted as six-week-old pad Thai in the office fridge.
Washington: At the first company I worked for (which no longer exists) I rose very rapidly to an impressive-sounding title and held a lot of responsibility but didn't make much money. After that I took a series of jobs that paid more but on paper look like demotions. Any suggestion on how I can present and explain this on a resume?
Titles vary from organization to organization, so this likely won't be as much of a problem as you fear. That said, one way to keep jobs from looking like demotions on paper is to use a "functional" resume, in which you group your skills in categories tailored to the job for which you're applying, as opposed to the traditional "chronological" style. Follow that with a list of the places you've worked, including titles and dates.
Adelphi: If I am told that I will be contacted for a second interview in a few weeks, should I still call to see how things are going? Being in a holding pattern for so long is getting to me.
Assuming you sent the requisite thank-you note, just wait. Distract yourself by continuing to look for other jobs. If the employer hasn't contacted you in two weeks, then call.