This trip should give you the opportunity to generate your personal gph/RPM/speed/distance graph or chart.
They use to say, 1/3 reserve but now, I keep hearing people say 20% reserve.
Plan your trip allowing for designated refueling marinas.
Depending upon your starting point, Stuart .... cross FL there. I am told there are fueling points on the cross FL canal.... I'm sure you can refuel at Stuart.
When you get down to about 1/2 fuel capacity, start looking for a refueling point.
Do you have sight glass on your fuel tanks? Mathematically you can calibrate your sight glass with blue and a magic marker if you have rectangular tanks. If not, make a note on the blue tape and then when you filled up. Between fill ups, try to maintain your RPM. After a fill up, raise your RPM until the next fill up. Always write down the number of gallons you took on board. If you get 1/2 dozen points, you can extrapolate, and generate your fuel verses RPM graph. In the future you can generate more points, refining your graph.
Yes, I know, I am ignoring sea state and currents.
So many variables..... give it your best shot.