Please tell someone who's working her way through the DG questline for the first time - if I side with the Dawnguard, is there any way Valerica's study will be accessible for me before I complete the questline? Please try to keep your answer as spoiler free as possible. Yes, I'm aware that Harkon is the Big Foe in that questline and that I will end up defeating him somehow, but I really don't want to know any details in advance.

I need a dragon bone, and my character isn't Dragonborn, which means no dragons in my game. I know there's a sample in Valerica's study, but if I have to wait too long to get it, I suppose I might just as well get myself one with console command magic.

You'll have to visit the study to complete the DG questline, no matter which side you choose. It's fairly early on, maybe at about the 1/3 point of the questline.

If you join the Dawnguard? Yes, you'll have to go through the study to advance the questline. As was mentioned above, you'll go there pretty early.

Ok, that's all I needed to know, thank you!

Another Dragon Bone is available thru the College of Winterhold, FYI.

Her study respawns after 10 days, so it is a good place to get rare ingredients and other items.

I know, but this character isn't doing that questline either. Only DG.