Yep, you can get the Tourist Octopus card at HKIA, the MTR counter in Arrival Hall.

Of coz not include other transportation rides than MTR. You can read thru the info in this website : http://www.octopuscards.com/consumer/help/...ts/en/index.jsp
It stated "Three days of unlimited rides on the MTR* (except on the Airport Express Line), starting on the day of your first MTR journey."

As it already said it's a 3-day limit of unlimited MTR rides, of coz after 3 days, your octopus card will be on "pay as you go" basis. So if you'd like to visit Macau, I'd suggest you go after the first 3 days of your trip.

Also, the tourist octopus card includes Airport Express Line (AEL) rides, so you should take AEL from HKIA to downtown so you won't waste the value... 

p.s. forgot to remind you that ferry rides from HK to Macau v.v. cannot use octopus card to pay, you have to purchase ticket by cash (or credit card, not sure) at the ferry counter at the pier. 
No, there is no ferry service from Macau to Disneyland Hongkong.

Yes, you have to take ferry to HK Island or Kowloon (Tsim Sha Tsui) then take taxi (if you can afford) or MTR to Disneyland.