I don't believe you have to be Dragonborn to get the Elder Scroll. You have to get the Elder Scroll to complete the MQ, but the Elder Scroll can be acquired before that.
Note: I don't have Dawnguard, but I think I had a character who had the Elder Scroll who never did any of the other MQ stuff.
I belive this is true, yes
I wish Bethesda would stop shoving the main quest down our throats, they have been doing this since Oblivion just let it rest. We should be able to advance in the Dawnguard or the Volkihar without having to do the main quest.
the main quest in Oblivion was by far more independent than the one in Skyrim, in Skyrim you cant even be part of the civil war whitout having started the main quest .