As long as you book a package, it will include the voucher for mini golf and some other things. Adding tickets later to a room only reservation will not make it a package. Online you can choose to book a room only or a package and if you call you can let the castmember know you want to book a package.
When you book a package online or by phone and you would book the tickets at the same time. However, it is possible to book a ticketless package and purchase your tickets from an authorized third party vendor, but you have to call. Either way, with or without tickets a package has very different rules from a room only reservation. A package requires a $200 deposit, final payment is due 30 days before arrival day and there are fees and/or penalties for any changes or cancellation within 30 days of arrival.