Membership Site Models: Montly Postings or Emailed Content?

I'm in the process of launching a subscribers-only area of in my internet marketing forum. My forum caters to newbies and beginning internet marketers in my niche. I intend to provide my subscribers with access to paid ebook content in addition to weekly IM lessons. I will also have special threads for productivity tools and an ebook library. Each month, the paid ebook access will change with new books offered but the tools and library would remain available every month with additions as they become available.

I have two questions:

First, should I plan on removing content each month or not posting content at all and using my autoresponder to mail new content to each subscriber every 30 days? I don't want to make the mistake of having everything available all the time and become a target for content scrapers. What has worked best for others in terms of managing subscriber content?

Secondly, do most find that a monthly subscription model works best or is a one-time annual fee the better route? I suppose that I could offer the one-time annual fee at a substantial discount in order to ensure the most profit but I'm open to suggestions.

Regards,
Ice