I've searched around the internet, and I get conflicting information, so I'm asking here for someone who has done this.

I am playing Dawnguard side. If I let Serana turn me, I imagine the Dawnguard and Isran will be.. unhappy. That said, can I cure my vampirism, finish the questline, and continue doing the sidequests? I'd like to turn Vamp for a while, but I don't want to ruin everything by doing so.

yes, If you let Serana turn you it will lock out all the quests for the Dawnguard temporarily until you are cured.

Thank you.. but once I am cured, I can do any and all? Just trying to be super clear, I appreeciate the reply.

Yes, you will be able to do everything from before you turned.

I talked to Isran as a vampire. His only comment was "Get out of here monster." No aggression, just a curt dismissal. So I cured myself (turned into a werewolf) and completed the quest line.