My Ezine Success Academy students and I had the opportunity to grill web designer Marcus Badgley, and here are some of his answers (in brief):

While there are no absolute rules (and no ezine design police!), he generally suggested a sans serif font for body text (like Ariel or Verdana). Headline fonts can be sans serif or serif. It’s great to have some contrast between the two.

Sizes go like this: 11-13 points for body copy, 14-16 for subheads, and 17-19 for headlines. (And that’s pretty much all the “levels” you should have.)

Color: Generally no more than three colors, which ideally coordinate with your branding; having two shades of the same color and an accent color to make some things pop is good.