Hi Chox
Jump on a train from the airport to the city centre. Its straightforward and comfortable. Pay at a machine in the station if you have coins at that stage otherwise you need to go to a booth with your fresh new notes.
We visited both museums you mentioned and just rolled up but if there's a special exhibition runningit might be advisable to book. Although Amsterdam can be busy but its not like London or Paris for volumes of people.
A good card to get is the Iamsterdam card. It covers your transport including a canal trip, and entry to most museums.
This is a good wesite for info. It aslo explains the Iamsterdam card.
http://www.iamsterdam...amcard/iamsterdamcard
Have a great time.