I want to play through Dawnguard siding with the vampires and such, but I also want to finish up the Companions quests and the like in their entirety.

How far do I have to go before being a werewolf is unnecessary to being a Companion? Do I just have to finish all of the quests until the end and get all the totems and then I can say bye-bye to the pooch or what?

You can not progress the story line unless you become a werewolf. You can however cure yourself of it when done and still remain harbinger/all the benefits as if you remained a werewolf. Aela will only give you the gift one more time should you change your mind later on.

I would say since you can become a vampire as many times as you like, do the dawnguard first, companions second, then either cure yourself or just have Serana turn you back into a VL.

Thanks. I didn't realize that I could become a vampire lord or werewolf again after "losing" it.

This makes everything so much simpler!

Or do the Companions first and then, the Vampires.