New blogs await a final click from a Site Admin to Activate. Keep blog registration enabled and open, keep SiteAdmin email notices enabled, and this keeps new blogs queued in SiteAdmin–>Blogs “Awaiting Moderation”.
First, enable “New Blog Moderation” at Site Admin–>Options. Then, SiteAdmin–>Blogs: New blogs have activation link “Awaiting Moderation”.
Install: drop it mu plugins.