1) Where in the caribbean should I cruise? Eastern, Western, Southern, other??
The answer to this depends on what you are interested in doing. If you want to find the party area's or you prefer snorkeling and scuba or want to just lay on beaches. Even though many areas in the Caribbean are similar each does have some different things to do. Your group will have to decide what is the preference.
2) What is the best ship to cruise on for the caribbean (ages 25-30)?
For that age group I would suggest either Carnival, Royal Caribbean or NCL for the best cruise lines. Keep in mind NCL is freestyle cruising. Carnival and Royal Caribbean deffinately would have people more in your age group even though they will have all ages onboard.
3) Who should I book through?
If you are going to book as a group, find a good reliable TA that is willing to discuss your needs and see what extra's they may be able to get you. I would not deal with an online service unless you call them direct and have a specific contact person and are able to get a hold of them on a frequent and short notice.
4) Any other advise?
Depending on the size of your group, it is NOT always cheaper to get a group rate. Have whatever TA you deal with check into individual pricing and group rates so you can decide which deal you want. Have as many people as possible in your group ready to make a firm commitment to the cruise as well as the means for a down payment or full payment to be made once a decision is made on what cruise to go with.
5) Do cruises offer drink packages?
Some cruise lines have cruise coupons to buy. All cruises have specials of the day for lower prices. The high end lines have drinks included but the high end lines also have a high end price.
My best advice is to discuss with your group what they prefer to do on a cruise and than contact a TA and have them sit down or talk with you by phone to discuss this information so they can try and find the right cruise for you and the best deal for you. That is what their job is. If you do not feel the TA you first talk with is providing you with good information I would find one that will work with you to your and the groups satisfaction.