I have a lvl 50 elf, and I've been avoiding the main quest so far and haven't talked to the Greybeards yet.

In the Dawnguard DLC, my next quest for the vampires is 'Discerning the Transmundane' a late game main story quest.

I don't want to make the mistake of playing quests out of order or potentially break my game.

Can anyone offer suggestion?

I have just came across this right now and was wondering the same, I don't mind breaking the main quest as I won't play it but will I be able to get the dragon elder scroll?

I was curious about encountering dragons in Dawnguard before I had started the random dragons for the main quest as well. So just to be safe, I killed the one at the tower before starting Dawnguard.

Still curious if you can do the whole DLC without having started the main quest.

You can do Discerning the Transmundane without touching the Main Quest. Getting the Elder Scroll before you are directed to on the Main Quest will not mess with your game.

Was about to inquire about this myself... thanks for the heads up.

That is awesome! I was worried about breaking my main quest when i did this. But what about people who have finished the main quest and turned the elder scroll into the orc at the college? Can you get it back for the dlc?

Yup, talk to the orc you sold it to, Urag gro-Shub.