I went cruise with Carnival 3 years ago

1, sea sickness is not very bad, you can buy some Gravol tablet or some patch (behind ear). and you can have some ginger with you.

2, yes, there is shuttle bus from airport to the cruise, you pay it while you book your cruise.

3, there is food 24hrs on the cruise, it is free. you have to reserve dinner restaurant seat if you want to eat there (dress well). there are all kinds of delicious food abailable, pop  (except Coca) is free, you have to pay for alcohol.