do i need to do the dragonborn mainquest to do the dawnguard mainquest?

i always hear you get this shout and that shout, but i can't find anything that tells me if i need to be dragonborn....

this is very important to me, because i really only do the mainquest on new characters, because i heard a while ago that you need to do it.

No you do not. In fact, given the NPC killing issues introduced by Dawnguard, I strongly recommend you do Dawnguard ASAP with a new character.

Why? Do the random town killings stop after the Dawnguard MQ is over?