How do I require a certain Level to access various parts of BuddyPress?
What you can do is use URI Restrictions.
See: WordPress Dashboard → s2Member (Pro) → Restriction Options → URI Restrictions (typical w/ BuddyPress)
That will allow you to define specific URIs that certain Membership Levels can access. For example, to require Level 1 to access
/groups/ you would put
/groups/ in the Level 1 field.
Tip: If you haven't already, I recommend watching the BuddyPress + s2Member tutorial video.