I am having my cruise wedding coming up in January 2009. The best place to look up the cost would be the royal romance brochure, not all the prices are correct but it gives you a good idea of the costs. To answer your questions
1) there are three choices to choose from: Buffet with drinks ($48 pp), formal luncheon($48pp), or the hors d'oerves w/ open bar ($32). There is only one wedding party allowed at each port to have a two hour reception, everyone else has 1 hour receptions.
2) As the weddings are only allowed while the ship is at port, and they usually leave at 6pm, the weddings are usually lunch weddings. I found that I will not know the exact time of the wedding until two weeks prior, however you can request a time of the wedding. I am hoping to request in the late afternoon, maybe between 3-5 so that my guests can still hang out at montego bay before the wedding.
3) I do not know too much about the ships, but I do know that the newer ships are excellent, but you have to pay a little extra (150 for Voyager of the Seas) to have the wedding on one.
4) You have a choice of getting married on the island or the ship. Even though the islands look gorgeous, I chose to get married on the ship for less hassle and in case there is in issue getting all the guests onto the island.
So far I have 32 guests coming along with my fiance and I, and the cost was a little under 5,680. This includes a stacked cake, two hour photography, hor d'oevres, microphone and light set-up, flowers for the entire wedding party (orchards and the deluxe tropical bouquets), hair styling, and the inital wedding package cost with many extra bonuses. As the average wedding is now costing 28,000 this is a steal for a great wedding. Call Royal Romance, and make sure that you speak to the same person each time or it can get a little confusing. I have been working with Shantel, and everything has been great so far. If my wedding turns out as easy and great as it has been planning it, everything will go perfect.
P.S. Be sure that you set up everything with them, because even though they have helped me with everything I asked for, they don't do anything until you say it. And you won't find out a lot of details until you ask them since all the ships are different there are differect circumstances.
Good luck planning!!