Hi, Melissa!
What a fun way to spend time with your best friend and your daughters! A girls-only cruise...and it's your first? Even better! You couldn't have picked a better experience than Disney Cruise Line.
As far as gratuities, you can handle this on the last night of your cruise through Guest Relations, or you can prepay before you leave or before the end of your cruise. I recommend the latter since lines at Guest Relations can get super long on the last evening. You can charge gratuities to your stateroom, or you can bring cash on board. There's a great
chart in the Planning Center to give you an idea of amounts and who to tip.
As far as spending money, it really depends on how many nights your cruise is and how many times you'll go ashore at ports of call. You won't need cash on board, but you definitely will want to have some (or a credit card) if you plan on shopping or eating on your own at a port. I always like to have cash in case I get in a situation where I will need to take public transportation or a taxi, too. Plus, I like to have singles for tipping a room service server on board. I hope that helps you.
Have a wonderful day and a magical vacation. Bon voyage!
Andi