This was my first B2B cruise; did the 8N followed by the 6N(my 30th and 31st cruises)
Embarkation: I arrived at Miami airport where Carnival has a check-in counter in the baggage claim area. They tell you to collect your baggage prior to check-in; however, unless you are taking a Carnival transfer to the port, check in first and then collect your bags to avoid the crowds that gather following baggage pick-up. Once you check in, once you get to the port terminal all you have to do is show your room key and you will go right through. Very simple and painless.
Cabins: Booked an inside cabin, no issue except it was on deck #2 in the rear and you could hear the engine noise every time we docked; also the walls seemed very thin as I could hear my neighbors every so often late at night and early in the morning; otherwise I was a happy camper.