Contract Web Writer / membership coordinator?

I've been freelancing as a web designer for a little less than a year now, just building a client base and expanding my skills. A couple of months ago I got hired part time to rewrite content and update a professional group's website. Now they want to bring me on to maintain the site as well, specifically the calendar, newsletter, mailings, and other things the boss can't be bothered with . I'll be working remotely, though, so we have to write up a new contract.
I'm full of questions now. Here's a couple.
1) What should I charge for membership coordination services?
2) What should I be sure to include in my contract?