Oh yeah, one time I forgot to remove wine from my luggage (you are allowed to bring 2 bottles but it has to be removed and checked at boarding). They took the wine and left us a note in our state room that it would be available at the restaurant if we wanted to drink it for a corkage fee.
Yes, but they have drink packages you can buy. If you intend to drink a lot, you get the package. Can't speak for all cruise lines, but the ones I've been on have different levels where you get drinks up to a certain cost for free, like $12 a drink. That price and below are free, anything above it you pay the difference. Higher levels cover a higher price per drink.
Yes and no. Kind of the same deal as the what the TSA does. Your luggage will get scanned via X-ray or whatever, then it's up to the person looking at the monitor to determine if it needs to be opened or not.