If the regular season was 16 weeks long then I suppose there would be 16 games per week.

From what you're saying, I'm guessing the season is longer than 16 weeks, so teams get an extra week off from time to time.

Right, each team gets 1 week off, though some teams get the week off as early as Week 4 and others later. So there are 17 calendar weeks in the regular season, and then playoffs in January.