Thanks for all the answers. I have been kayak fishing ~1 mile offshore and really haven't pushed farther than that. The boats Ive fished on have pretty good luck under 4 miles out so I would say 10 miles? or so justttt in case. When I said minimum, I really don't plan on going out in choppy conditions so I said what would hold in 15-20mph winds (I assume you gauge on the swells, not winds, but that's what I do with kayak fishing so really all I have to gauge with) just in case I got caught in that.
Would like to be able to have 3 people on board, comfortably. And I see a lot about tank size relating to distance. Cant you just carry extra gas? I didn't realize boats got that terrible of "gas mileage" hah not cool.