I'm playing one who is a serious Dawnguard member. She lives in Lakeview Manor with her husband Sondas and children. Every Morndas she goes to the Dawnguard HQ to get a quest. I let her do one other quest as well, if possible. After four days she heads home and spends Fredas to Sundas with her family. She's slowly working her way through the Dawnguard questline and main quest line right now.
I got around the whole Serana issue by pretending that my vampire hunter has visions of the future, and so knows quite well Serana will not ever attack her or anyone she loves. In fact, knowing before she met her that Serana would be so enraged after herself and Sondas are brutally murdered by some vampires that she would decimate Skyrim's vampire population in vengeance did an awful lot to reconcile her vampire-hating soul to the idea of a vampire best friend.