I would personally go the ebook route, getting people to sign up for a recurring membership to a site that may or may not be frequently updated would probably be the biggest hurdle.

A one-off payment for something they can download and keep is much more appealing imho.

Regarding the piracy issue, try ways of dynamically creating a PDF that will embed the users name & address in the footer of each page. Seen it done before and can act as a deterrent.