DCL liquor rules are DCL liquor rules no matter where they are sailing from. Same rules will apply.
Check in was a much to be desired. When we arrived there was a customs form they were handing out that was not on the DCL website for you to fill out. So there were hundreds of people trying to balance on trash cans, wall, each other trying to fill out this form. Check in was almost TSA like. One person at a podium looking at your ID and then you go through the metal detector and xray your bags.
There was no signage for the Platinum/Concierge check in but I knew enough to ask. My parent however did not and they were directed to the regular line even thought they said they were sailing concierge. They stood in line for going on half an hour before I arrived and called my mother to see were they were. Not that huge of a deal except my father had had heart surgery four month prior and should not have been standing in a line like that! So they went to join us at the counter, but it was insisted they go to a different agent to check in even after I told them we are all in the same cabin. So then our agent had to keep running to the agent checking my parents in for whatever reason to do our check in. She then wanted the customs form we filled out earlier, only the TSA like podium person took it from us and they made us fill out another! I was hugely annoyed at this point. Check in had now taken three times as long as it had for me at PC. Also the terminal is much bigger. At this point I wish I had a wheel chair for my father. Once we were on board, it was all good from there.
Can't help you with drive vs. stay over. Driving in on a weekend morning was easy peasy. If it was a weekday it might have felt different.