Here is some data from experience to help with your question: over to you to "do the math". One gallon of diesel will run a Webasto 3500, 12,000 BTU (furnace type) heater for about 10-11 hours. This is from personal experience that also happens to match the manufacturer's claim.
s/v Auspicious - if you are out there - weigh in please. Dave has "wintered" in Annapolis harbor using (I presume) one of these.
We ought to ping Cracker Jack, who has more experience than I do.
I spent one Spring in Sweden, one Winter in Washington DC, and two Winters in Annapolis using a Webasto 3500. I have one winter in Annapolis using an Espar D5. Fuel consumption definitely depends on how cold it is and I expect on how well insulated your boat is.
I run between 1/2 and 1 gallon diesel per day during the cold months. I spend at least a couple of hours a day with the heater cranked up and some hatches cracked open for ventilation.
I carry 120 gallons of fuel and try to stay topped up through the winter. At the moment I'm down to about 20 gallons and waiting for ice to clear off Back Creek so I can get to the fuel dock. If that doesn't happen in the next week or so I'll start jugging fuel.
I'll try to check in regularly in case you have specific questions.
I will say that based on hanging with other liveaboards, forced air diesel heat would be my choice again, followed by diesel hydronic, then electric (which means being plugged in somewhere and subject to utility failures, followed by propane (wet) or wood (messy). YMMV.