Yes

Yes or by octopus card

You will have to disembark and re-join. I did not travel at the time you ask about but it is a smooth operation and so I think you will be able to flow with the commuters.

There sure is a taxistop. Taxis are cheap compared to european prices. You’ll probably pay 5 to 8 dollar/euro for your taxi.

Buy a tourist octopus card. Great value.

Sorry, I don’t know as we never visited Disney, however the MRT stops at Disney.

Yes, it seemed easily accessible to the ferry by wheelchair. But on the other hand, I did not see anyone in a wheelcahiar using buses and subway in Hong Kong.

There are ticket counters located on the piers where you can easily purchase the tickets. Alternately, I suggest you use the Octopus card, which is a stored value card that you can buy at any MTR station. You can store money in the card and use it for all your travel in Hong Kong, including MTR trains, buses as well as ferries. You can have your remaining balance refunded at any time by returning the card at any MTR station.

We bought single tickets. They only cost 2.7 Hong Kong dollars which is less than 50 US cents. There is a machine that takes cash on the pier. It is very easy and simple. Ticket machine gives change.