Transport to and from HK Airport and Novotel Nathan Road Kowloon Hotel

We will be going to HK for a short holidays 11-14 Jan 2018 and we will be staying at Novotel Nathan Road Kowloon Hotel. Can advise what bus shall we take from HK Airport to our hotel?

As for the return, from Novotel to HK Airport, we consider to take the express train from Kowloon Station to HK Airport, can the train ticket be purchased online and in advance?

Thanks

Joanne from Sabah, Malaysia.