Do we have to make reservations? There is 5 of us.

You can pay online or cash at the entrance it really dosnt matter you pay at the same place where you check in and the train has plenty of seats, I think it leaves out like every 30 mins or so

You don't have to but it is a lot simpler I would go online and make the reservation. Also make sure that you bring cash they do not have any type of credit card payment access at any of their vendors

Yes

Your best bet is to go online and pre-order