Haven't been on Carnival but from my experience on other lines:
a) You will put your luggage outside your cabin on the last evening (so keep a small bag to put the things used overnight and carry that off with you). The ship staff will collect your luggage and off load it for you.
b) If you prefer (and if offered) you can do self disembarkation which means you carry all your own luggage off with you without assistance and so you do not put the bags out the night before.
c) You usually have to have vacated your cabin by about 8am. Depending on what time the ship arrives and clears formalities, disembarkation can begin about 7 or 7.30. Groups are called by colour usually based on deck. Usually everyone is off by 9.30. If you need an earlier disembarkation than you are allocated, you can go to guest services and have it changed. Better to do this than just try and leave early as your luggage may not have been unloaded otherwise.
d) Once you are off you will collect luggage and go through immigration.
In terms of what time to allow, we usually only book afternoon flights, even though we may end up at the airport a bit early. We like to have the leeway in case anything unexpected happens. If the port is well organised you may well be off and have cleared immigration by about 9am (assuming the ship arrives about 6 am). The cruise documentation will usually give guidelines about what time to make an onward flight booking.
Is the line offering transfers at the end as that can make things easy for you?
