That’s pretty much how I would approach it too. I was looking at customized sea adventures recently and found
https://charterclick.sc/ useful for getting the basic options together before making a decision. You can compare different yachts by things like guest capacity and charter duration, and there are also options involving a skipper. I liked that this makes it possible to think about the trip around the group rather than choosing a boat first and trying to make the plans fit afterward. Once you know roughly how many people are going and how long you want to be out, the available choices become easier to compare.