Yes, you can pay tips in advance by calling
DCL and asking that they be put on your credit card. You can do the same thing while on the ship--they are billed to the CC you put on your onboard account.
I bring very little cash...typically about $150. Almost everything can be charged. Hotel check in, rental car or DCL transfers, any LARGE purchases on the islands. Some places do have a $15 or $25 minimum purchase to use a charge card. The vendors at the various booths outside will take mostly cash...and you can't bargain for price if you have a credit card. I'm one who made a credit card purchase and had it charged in Bahamian dollars and included an exchange fee from my bank. Never had this on any other island.
You will need some small bills to tip the baggage handlers if you're not using DCL transfers. If DCL takes you from MCO to the ship, you won't even see your bags. If you will use the porters at the terminal, you'll need some tip money for them. People here talk about tip money for room service, but in actuality, you can put that on your onboard account as well--you sign the slip and indicate the tip.
Every port in the Caribbean takes US dollars--gladly. The only quirky thing I encountered was a sign in the post office on Grand Cayman stating that they could give change in Cayman money only. They happily took my US money to mail postcards (25 cents each). Since I had change, no problem. The post office on Castaway takes only cash. (65 cents for a postcard last time I sent one).