you'd get "hooked" on cruising! From looking at the deck plans, a 6B would be fine IMO, unless it's one of the forward cabins. There is usually more movement forward. If this doesn't bother you, great
On the ship you can use your credit card when you board to pay your Sign & Sail or you can deposit cash (dollars) when you board for all your onboard expenses, including ship sponsored Shore Excursions.
At the ports in the Med I think
you will need to change your $$ to the local currency for shopping or non-ship excursions.
Sounds like a great cruise. Have a wonderful time!