It looks like you've received some good information, and that you're pretty much set for your cruise. As you pointed out, NCL does assess a charge of US$10 per person per day as a service charge, which includes tips to cabin attendants and to all servers (dining room, buffet, etc.)
Since you will be using a credit card to guarantee onboard charges, the only places where you can use currency will be in the casino and the game room. You can even charge casino chips to your account if you like. At any time during your cruise you may ask for a printout of your current onboard statement at the main counter, so as to avoid any surprises on the last day or to correct any erroneous charges.
Enjoy your cruise, and let us know how you liked it when you return.
We've sailed on NCL 4 times, and have had few complaints. Keep that positive attitude, and I'm sure you'll both have a great time.