Can I enter China driving my own car and exit to Nepal passing through Tibet? What are legalities?

I am driving my own car with my wife. We have international driving permit and Carnet de Passage for our car. We wish to enter China from Laos and exit to Nepal. We plan to spend 30 days in China. Alternatively we can enter China from Nepal via friendship highway and exit to Mongolia. Can you suggest which is the best way? Is it compulsory that we must have local driver and/or guide?