Welcome to Cruise-chat, Stephan, and congratulations on your upcoming honeymoon! For newlyweds you are not all that young, but you will probably find yourselves among the younger passengers on a cruise from South America to Europe. That's ok - everybody will probably want to "adopt" you!
I don't know what you have been promised as far as the cabin and the food go, but some people find that their expectations are somewhat different than what they experience on a cruise. If you go with the attitude that you are going to enjoy yourselves, and overlook whatever details might not be quite perfect, you are sure to have a good time.
No one can promise a "quiet" cabin, as there is no control over what the neighbors will be like. However, I think it's a great idea for you to be looking at a verandah cabin. If you can, since it's a transatlantic sailing, you might want to consider booking a cabin that is amidships - in other words, about halfway between the front and back of the ship - as you are likely to feel less motion there. I would definitely recommend that you avoid booking a cabin toward the bow, as that's where most sea motion is felt. As long as you do not book one with an "obstructed view," you will have a good view from virtually any verandah cabin.
Unless you are into a specific brand of bottled water, there's no reason to bring one on board, as the water onboard is probably better than most onshore. Besides, bottled water is available for sale onboard ship; like all onboard purchases it will be charged to your shipboard account,which you will establish when you first board at the start of your cruise. Be sure to bring a valid credit card for that purpose.