Basically, when you are once onboard and have your ship board account in order, it is a cashless system, you use your card for any purchases, drinks, etc. Anytime you order a drink, there will be a 15% tip added to each drink, so that is not a part of the daily tipping. Yes, if those are prepaid, you don't have to tip your dining room server or cabin attendant, that will be taken care of.
Any drink packages you wish to purchase, you can do once onboard, they usually are pushing those, so it shouldn't be difficult to guy those if you want.
MOst of the time, you may encounter some rain, but usually doesn't last the whole day, so unless it is really bad, they won't cancel excursions.
Each evening, they will leave a daily paper in your cabin for the next days activities, so be sure to read through those for shows and times, etc...