Question about my flight trip from Vienna (Autria) to Shenzhen (South China) through Beijing Airport

Will arrive on Monday (04.03.2017) with Air China at PEK 6:25 AM (T3)...Then departure with Air China at 9:20 AM (T3) to Shenzhen International Airport. Will arrive in Shenzhen at 12:45 PM.

Questions:
a) Are 2 hours (6:25 AM to 9:20 AM) enough time to change the Air-Plane? to run through the obligated steps (check-out, check-in, Inspection, security check, customs inspection, waiting & boarding...)
b) How it works to find the right terminal or gate for the next flyt there? Are there some helping informations (service points...)?
c) If i have to take a transportation from one to another Terminal or gate (for example T3 to T2)..Where i can buy the ticket for this transport vehicle?
d) Are at the airport some possibilties to buy a prepaid SIM Card for using during my trip time in china? If yes where and how much does it costs?
It would be nice to get some helpful information....Thanks a lot for your effort.