What do you get from the HK$150 worth Octopus Card you buy from the Airport?

I will be arriving at HK Airport and will go straight to Macau by Ferry. I will stay there for 2 nights. I will take the ferry back to HK after. I will stay in HK for 2 nights as well. I plan to go Disneyland and perhaps go to interesting tourist spots in HK within the period. I will be buying an Octopus Card as soon as I arrive at the airport. I am planning to ride the MTR, the busses, etc. What card do I need to buy? Will Octopus Card with HK$150 work? I will be traveling together with my niece - who is 8 years old. I appreciate your answer. Thank you very much!