Hi Tink,
1.) The eMember is a single site license.
2.) Yes the integration is thought the eStore.
3.) The following post will explain how you show a teaser and selective content.http://www.tipsandtricks-hq.com/wordpress-membership/how-to-protect-a-section-of-a-post-or-page-88
You can also find more information about the eMember here: http://www.tipsandtricks-hq.com/wordpress-membership/
Ivy