User blog comment:Neowitch/700 - Breakfast at Mugiwara's/@comment-3119203-20130228042910/@comment-94.68.150.253-20130228150133

As it is stated exacty after the timeskip, Akainu "was so dedicated" that he tranferred Marine HQ in the end of New World, where G-1 was. So, when it says Red Line, it means the back side of Reverse Mountains. G-1 took the place of the old HQ and G-5 is the first Marine Branch after you entered in the New World.

About Dofy, we have not a solid clue that can prove his superiority over the rest Shichibukais, but we can assume that he is the one with the most influence.