Well, recruited Gunmar and Sorine. Then after they got to the Dawnguard Fort and everyone was hit with a blast of sunlight... I fucked off. Seriously. I didn't really like how sudden the quest was. Like you go from quest to quest to quest so rapidly. So, I took a break. I grabbed some Dwemer Schematics for Sorine, killed a vampire for Gunmar and got two more assignments from them before I decided, okay, go see what Isran wants. That left me time to you know, give Serana some time to think about what she wants.
Of course, I tried some of the sass responses. Like... to start, I could see Siddgeir asking about her importance over the Elder Scroll because he would be genuinely interested in why the fuck she's supposed to be important. But then of course he goes 'wtf do you want the Dawnguard's help for' and she sasses him. He doesn't really buy this shit and Isran is on the same page because seriously, she must be insane. But hey... I guess she's important.
I don't want to go find the moth priest yet. I still prefer to let him wander around a bit now that I got my armor. I'd like to enchant my Warhammer with something, fix my gear up, drink, patrol the fortress because that's what you're supposed to fucking do. Give it time before the moth priest comes. And during this time I can see Serana probably getting the cold shoulder from everyone save for him since he's just sort of neutral on this shit now. Dialogue can be exchanged between them. Obviously they wouldn't become BFFS FOREVER INSTANTLY like some people make it out to be but I'm sure after a while he WOULD ask why she's such hot shit.
Plus the whole "How on Nirn do you just give yourself up to being a vampire" and that type of talk because srsly. He could not fathom it. Like life sucks already. What's the point of making it suck forever. Also he would do some practicing with the targets. And playing with the huskies because murderous dogs fuck yeah.