Hi greengerm.
Can you get a Chinese visa for that length of time? I am a UK resident and we can only get visas for a month at a time. I had to renew mine while I was in China.
When I was in China, I used trains and buses mainly and only took one flight. It's very easy to get around using their transport system. I didn't take any fast trains but the latest line from Beijing to Guangzhou in 8 hours is... very quick.
I had to travel differently to other places I had been and that was because of the size of the cities and towns and because of the language barrier. To move from place to place, I used to book my hostels online from an internet cafe when I found them because they aren't easily identifiable from the outside, when I got to a new town or city I would find a taxi, ring the hostel and speak an English-speaking member of staff and tell them to give the taxi driver directions to the hostel. I did that because I had found out in advance that the taxi drivers might not be able to read so giving them a written address or directions won't always help.
The rules of travelling to Tibet seem to change. It changed a couple of times while I was in the area. You might be better to wait until you are there to get the most up-to-date info. The hostel staff are generally very good and they will have the information you need.
You might be travelling alone but you will meet other travellers (if you want to). I was fortunate to hook up with five other solo travellers. We travelled together for about a week and had a great time. We were very lucky because one of the travellers was born in China but grew up in NZ so he could speak Chinese.
Have a great time! I loved China. It is one of my favourite countries.