I'm also thinking about a new user's path. We require e-mail confirmation before you can login. That's necessary to prevent spam and trolls. But what if you would immediately be logged in after sign up, but couldn't post or follow before confirming the e-mail? Perhaps that would be better?
The "welcome" screen looks like a modal window, and a lot of people seem to skip it instinctively. What if it was actually a full page? Also, the contents of it really need to be revised.