

Mandarin is the most accessible and widely spoken, Cantonese is good if you want to spend a lot of time in the south. Good luck if you want to learn one of the hundreds of other dialects, maybe make a friend from one of the places and have them help you.
Those subway stations in the middle of nowhere that were being touted a while back now are surrounded by bustling cities. Planned infrastructure takes time to fill, but it works much better than suburban sprawl