So, I am at the part of "Dawnguard" where I have to get "Elder Scroll: Dragon" and "Elder Scroll: Blood".

when I start following the questline to get "Elder Scrolls: Dragon", the quest description mentions "Paarthurnax".


Now, I have not started the main quest yet, and don't plan to for quite awhile. will doing this quest suddenly break the main quest? Am I going to have to go beat the main quest before I proceed?

You're going to have to procede with the main Quest, as the Dragon Scroll is part of it.

damn...

This is false.

You only have to do the part of the MQ that involves finding the Elder Scroll. Essentialy, you go to a guy, he sends you to a cave, you get the scroll and continue with the Dawnguard storyline. You don't need to complete any other MQ quest. Nothing will be broken, when you decide that it's time to start the MQ you'll proceed as normal and only skip the quest about obtaining the scroll, because obviously you already have it.

On one character I did the entire DG quest line without ever doing any of the MQ (except escape from Helgen). I had no problems at all when I finally did the MQ and got to the part where Parthurnax asks me to get the scroll. The only problem with this was missing out on the cool dragon fight in the Forgotten Vale since there weren't any dragons yet.