Freeboard can be what you are comfortable with. Having said that I once took a ship 5 miles off shore to an oil rig after a hurricane with the decks awash. Perfect day no sea and knew I would be there in 2 hours or less. Would I cross the Atlantic like that - no way

the point is what are you going to do with it. The very generic rule would probably be that buoyancy / reserve buoyancy; is one and a half of what you need. Do you paddle by yourself with no gear? Do you haul gear out to remote locations? do you paddle with others where you might have rescue someone else. Buoyancy of 1 inch is great if you never add another pound of weight

Tons per inch or in this case pounds per inch of immersion is a fun figure to help you

Also remember freeboard adds wind something - weather cocking, drift etc.
So .. try and understand what your real needs might be over the life of the boat and have fun