Butlers are sort of super-charged cabin attendants. They will do almost anything you ask. For example, take care of your laundry and dry cleaning, bring your room service orders, make reservations for specialty restaurants, etc.
I once had a butler zip up the back of my dress because the spousal unit was already in the casino.
I don't know about RCI, but on Celebrity the butler also brought tea sanwiches and sweets around 4 PM then "sunset hors d'ouvres" around 6 or so.
The tipping schedule is the same as for your cabin steward, but we add more for "above and beyond". Last cruise we were going to miss a self-booked shoreX because the young woman handing out tender tickets didn't understand "priority" so we didn't bother to hurry. Our butler, when he learned of our plight, hustled us straight to the head of the line. He got a REALLY good tip.
You're in for a fabulous cruise. Be warned that the crossing of the Tasmin Sea can be rough. Take some ASA 800 film for Milford Sound, in case it's foggy/rainy. In Sydney, Paddy's Market is THE place for souvenirs. Everything you can buy downtown is there at about half the price.
For sure take the film camera along, too. These may be sights you will only see once and it's great to have backups AND photos with better resolution. One of the most awesome sights in the world is coming into Sydney Harbour at sunrise.
The only souvenirs we bought in NZ were t-shirts. If you walk up the "main" street (it's easy to see which one it is from the pier) there is a mall on your left about two or three blocks up. There was, when we were there, an excellent T-shirt store in the mall. High quality, good prices.
Paddy's is THE place for souvenirs. It's not near the pier which is on Circular Quay. However, there's a bus stop right there. The buses in Sydney are "jump buses" (same thing in Aukland) where you buy a ticket and jump on and off at will. You want to look at a map of the two bus routes to make sure you're going where you want to go. I believe the stop for Paddy's is called "Chinatown" but don't take it to the bank.
Don't be afraid to ask anyone for help and directions. Apparently rudeness in large cities is limited to the Northern Hemisphere.
Let me know if I can help more and just how much room there will be for me in one of your suitcases.