why does he need to go to NY to do the mixtape??
Who said anything about him going to New York to do the Mixtape? Yes, we know that they end up in New York but I very much doubt that trip will have anything to do with the Mixtape.
The thing is with OUAT we cant say we know things with 100% sure, the mixtape may or not may be related to NY, but since the episode name has a sort of connection to Neal, since is a song that Henry only knew bc of his father, neal`s apartment may appear again( really hope not, no more bait/fanservice neal related, that should ahev been done on S3b and s4a) and with Henry in NY, i say there is a chance the mixtape being related to NY trip. But we will have to wait and see if is or not related to Ny trip.