1. You can do that.
2. If you don't use a purchased ticket, it will remain in your
MDE (not DME) account.
Before you go to a park gate on your upcoming trip, stop at any Guest Relations and ask that
the
Ticket priority be set so that the park gates will only USE the ticket that you WANT to use.
3. Well, if you go to WDW after a ticket has expired, unused, you will be able to use its original
purchase value toward buying a new ticket for use on that trip.
Write down and keep that unused ticket's number and store it in a safe place, as it will
become "invisible" (to YOU) in your MDE after it expires.