Hi arie,
We
knew 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!