What’s the minimum number of guests to put up a boat trip?

There’s not a minimum number of guests. We can run a trip with just a couple of guests as long as they pay for the trip costs. But a bigger number of guests will make the price per guest cheaper.
Under 8 guests the price per person becomes expensive, so we recommend 8-10 guests for a good compromise.
Usually the maximum is 10-12 guests, depending on the boat.