do a search for Captain Marvin and i am sure you will find his web address. We used him and had a great time.
Aft cabins are very popular because you get a larger balcony.
The only time i really felt any type of engine vibration was when the Captain used the side thrusters to either come into or leave a dock.
There is always a gentle motion (you are on a moving vessel in a moving body of water)and a gentle humming of the engines.