^Watch out for that Cullen bug. Sometimes it's just a case of him not loading properly (easily fixed with a reload, or leaving & returning) but sometimes he can be permanently lost.
What's supposed to happen is that at a certain point, you'll go to his room and there'll instead be a messenger waiting and talking to them triggers a cutscene. However, if you do Sera's "pranks" quest while that messengers is in the room, it can cause a bug whereby when to come to talk to the messenger, the NPC interact icon won't come up and Cullen is effectively gone.
Not to spoil nything but that can be a significant problem later on since there's a fairly important quest that has to eb turned into Cullen to progress. The only way around it is to reload to before Sera's quest, so as a precaution, it's always advisable to go visit Cullen before Sera.
I got really lucky there. I did the prank with Sera with the messenger in the room, but fortunately, she was still interact-able with after so I got him back.
(On a side note, I know there's a comment that your character makes if she's gone through the romance scene with Cullen before you pull the prank, but there doesn't seem to be one with Jo)
I've just done the Wicked Hearts quest. I didn't quite get the result I was hoping for but it went a lot better than I thought it would so I'm sticking with that for this run through.
I was thinking a lot more stealth would be involved (and I usually suck at that) so I'm reasonably happy with managing to get out with 77 on the approval rating. (With a human non mage rather than an Elf Mage it would have been a little higher)