A few comments, but dont shoot the messenger
If you have a mortgage and house insurance, you probably need a backup conventional heating system.
A conventional house no matter how tight is going to have a pretty hefty design heat load and that means someone has to be there 24/7 to keep the place warm with a woodstove during the coldest times of the year. There are zero net energy and passive homes built in Mass that can go days without any heat input but might as well burn your house down and start from scratch compared to trying to do it with a conventional home.
IMO the only way to go oil free is to do what I and others have done and that is installing a indoor wood boiler with thermal storage or a pellet boiler with bulk fuel storage if you have a bulk pellet dealer nearby that delivers them in bulk with pneumatic system. Both are a $15, to $25,000 hit. (Currently the only indoor wood boilers that meet the EPA standards are gasifiers so use wood boiler and gasifier interchagably). Cord wood can cost less if you have a place to cut wood or willing to scrounge wood. Some members do well by talking to trees services and getting it for free or for low bucks. This requires dedication and time and I suspect most of us who burn wood do it partially for intangible benefits. A Pellet Boiler takes far less homeowner time but costs more to buy the fuel. Wood boilers do not feed themselves and when it gets really cold, they will probably need to be run once a day to boost the storage temp up, a pellet boiler with bulk storage and automatic feeder can go for weeks, its the closest thing to an oil boiler. The only gotcha with a boiler that uses bulk pellets is there are not a lot of sources who deliver bulk pellets, the big heating distributors that are snapping up local and small heating fuel suppliers do not mess with pellet deliveries and some folks have been stranded with no supplier when the local guy sells out. Do your research.
BTW note I was specifically referring to indoor wood boilers, I will refer you to a state website on Outdoor Wood Boilers
https://www.mass.gov/guides/heating-your-home-with-a-wood-burning-appliance. No matter how "clean" it is, an OWB is going to be heating the outdoors and the ground while an indoor wood boiler, typically in a basement, means any heat radiating out the piping and boiler casing goes into the house.
The good news that you probably do not want to hear is at 500 gallons of oil per year, you can pretty well solve the oil tank leakage problem by installing a Roth type oil tank
https://www.roth-america.com/product/oil-storage-tanks/double-wall-heating-oil-tank/. They are double contained with a lifetime leakage guarantee. The fuel supply system from the tank to the boiler is modified so that the oil is pulled up from the tank instead of draining by gravity out the side. Any heating oil company can make the switch in about 4 to 8 hours. The biggest limitation is if you can get the oil one out and the new one into the basement. The other thing you can do is replace your boiler with "low mass cold start" boiler. A typical older boiler stays hot year round, that means a lot of wasted heat during the summer, spring and fall when the heating demand is low. One company pretty well owns that market and its Energy Kinetics who make the System 2000. It uses a conventional burner so a typical service tech can work on it. Its likely that there is supplier that offers a biodiesel blend of heating fuel in your area and as the years go on I expect the blend ratios will go up. My guess is a cold winter in New England may finally force some new pipeline capacity to built into the region so Natural Gas will probaly replace heating oil but its guess at this time as the US government needs to swap over the nations housing stock to electric heating away from oil and gas in order to meet climate commitments.
The other thing to consider is that there are going to be lot of incentives to install minisplit type electric heating units. They are hassle free but with the current electric rates in Mass I would be hesitant to recommend them as a primary heating source but thrown in with a mini split is that they are super efficient air conditioning so if you cool you house in the summer the savings can be used to pay for the higher bills in winter.
The Mass Save and equivalent programs are a great program, but they are going for the "low hanging fruit", There are ways to further reduce heating demand in an older home but its starts to get radical with long paybacks. Cutting your 500 gallons in half would probably require gutting the interior or exterior walls, foaming the existing exterior wall cavities then adding a couple of inches of insualtion board on the inside or outside, major insulation in the attic, removing some windows on the north and possibly east and west walls and replacing the ones that are left. This is serious move your stuff into storage and go way and live somewhere else for a few months type of work and given the shortage of trades and big demand for new housing in Mass, it would be very hard to find someone who would even do the work.
BTW, I have a 1987 Full Dormer Cape in Northern NH with 6 inch walls, good window and fairly efficient construction for the era plus a Mass Save equivalent retrofit about 10 years ago. I have solar hot water so no need for hot water from the boiler. The two years prior to putting my wood boiler with thermal storage on line I was burning around 300 gallons per year with a "hot boiler" that was shut down in the summer and a wood stove I used on weekends. I havent used oil to speak of in the last 6 years. I go through 3.5 to 4 cords of wood a year that I cut and process myself. My wood boiler is an "ancient" 1980s vintage wood/coal boiler that was probably based on a design from the 1930s. If I went with a gasifier and bigger storage, I could probably reduce my wood use by a quarter to a third. I also have a Roth oil tank I bought off craigslist waiting for me to get motivated to install it to replace my 30 year old steel heating oil tank. If I am not home to feed the wood boiler, the system automatically switches back to oil with no intervention on my part.
