The last answered question I've seen about Tibet was from early 2015, and things change frequently around there. My preference would be to take a train to Lhasa from somewhere in China (flexible). I plan to do this in November 2016, staying there 3-4 days, and then fly to Shanghai or Xi'an. I'm a US citizen already have a Chinese tourist visa.
My questions, preferably for someone who had recent (2016 or late 2015) personal experience going there from China (please no Nepal-originated itineraries, the set up is very different), or heard from a trusted source:
Is it possible to prearrange the trip that I fly into China, and go to Tibet the next day (i.e. not having a 4-5 day wait)? If so, how does an agency organize the permit, you send passport details in advance? I was told you need to send your actual passport to China by mail for that (and receive it back of course), which doesn't sound like something most people would do. If you can share how much it cost you, this would be appreciated as well.
How comfortable was the train ride for you? Are there compartments for a single person, or they're all for 2 or 4 people? Do those fill up early, or could be booked next day?
There is a rumor that foreigners have to be accompanied by tour agent "at all times". How does it work in reality, are you being walked around North Korea style, or it is more a formal requirement, and you can still wander on your own?
Are other permits needed to travel outside Lhasa (day trips), and if yes, could they be organized timely in Lhasa, or everything has to be prearranged in advance?