I'll try to answer some of the last questions about liquor to the best of my knowledge, so someone please correct me if I'm wrong.
I don't think they offer a mixed drink package, but if they did, I would definitely be interested! Those drinks of the day sure add up. As for mixers, at the drink station they have soda and on my last cruise January 2010, they had Hi-C pink lemonade, no juices. However, they had some juices in the Topsiders/Beach Blanket buffet and dining rooms, but both have limited hours, so if you want other juice mixers, margarita/daquiri mix, etc, you are better off bringing some of your own to have it in your room on demand. Sometimes I wanted to make a drink and I'll admit, I was too lazy to walk upstairs 2 decks to get a mixer from the station lol, so it is helpful to have a small supply in your stateroom.
I don't think you can ship alcohol via UPS or another carrier. Even if you could, it would be costly due to size/weight, and I'd worry about breakage, and most of my favorite liquors dont come in plastic. This is why renting a car is such a great option because it gives you the freedom to stop at the liquor store, grocery, or anywhere else you need to pick up stuff that you couldnt fly down with.
I don't know if there is a restriction on how much you can bring on board.
DCL technically doesnt even say you can bring alcohol or other beverages on board. It says right in your paperwork that coolers and beverages are prohibited. However, it has been and hopefully will continue to be an understanding that DCL lets coolers and alcohol slide. I hope there is no limit as I inted to bring several bottles to last for this 2 week cruise!
I have brought on liquor purchased in Nassau and in St. Thomas before, so I'm guessing you can bring on liquor from other ports and you are allowed to keep it and consume onboard, unlike liquor bought on board from the duty free shop which is not given to you until the last night of the cruise to take home with you. If someone has been to other ports that they dont allow you to bring purchased liquor onboard, please let us know.
Hope this helps!