Very much believe the "You've got me, who's got you?" title is a reference to Watchmen, with its famous line "Who watches the watchmen?" To raise the question of who protects the ones who protect. As for the poor Midnight Ranger, obviously nobody :(

Actually the feeling I got from Joan's comment on "a woman did this to you?" wasn't 'wow how did you let a woman get the better of you?' but rather a sort of mildly pleased smugness.

Haha yes! Now I can let my mind be at peace :)

Wait - now you've made me paranoid. Joan said Andrew was on a plane to Copenhagen, which is the capital of Denmark. So of course Sherlock would know he's going to Denmark. But now you've said you can't comment and I'm getting all sorts of wild ideas about Sherlock having ulterior motives after all.

Joan said Andrew was on a plane to Copenhagen, which is the capital of Denmark.

Not a fuck up or mistake at all. Joan said Andrew was on a plane to Copenhagen, to meet Magnus. Even if she'd only said that he was meeting Magnus, Sherlock would undoubtedly know where his acquaintance lived (or even as Andrew mentioned, his name is very Danish), and can infer that Andrew would be going to Denmark.