Hi,

You don't need vouchers for the Limo service. At DXB, as soon as you've picked up your baggage and leave the arrivals, there's an office off to the right (it's well signed) where you go and get your limo. They'll also confirm your pickup time (normally 2 hours before departure).

There will be an Emirates representative at SYD who will direct you to your limo, or at least the limo driver will be holding a card with yor name on it.

As for Vienna, not sure how the 'water limos' work

Cheers,
Rick