Before going off-grid, you have to understand and rationalise your electricity usage.

Identify the large loads, the times of usage and how essential they are. If it's mid winter and the battery bank is flat and the 'oid needs some maintenance before it will start - will that be a major problem? Would you have a backup for that eventuality?

The bottom line is that a Listeroid will use about a litre of fuel to produce a kWh of electricity.  Some do better than this,  perhaps 1.5kWh per litre or even 2kWh - but that is exceptional and not the norm.

So you have to ask yourself whether you want to translate a 900kWh per month electricity bill, into what would potentially be a  160 US gallon per month fuel bill  (assuming 1.5kWh per litre).

Whist you can run the Lister on veg oil,  used motor oil or HHO with extra lubricant added,  you need to appreciate that the 10/1 could be consuming about 5 or 6 gallons per day.

The 10/1 'oid should produce about 10kW of recoverable heat for your CHP system.  From my experiments here with exhaust gas heat extraction and from the coolant, I found that 1kW per horsepower is a good rule of thumb.  This is approximately 1/3rd of what your 97 k BTU/hr  heating system currently produces.  However you will find that you seldom use the full output of your furnace, and you may find that the heat losses from your house in winter are within the capability of a 10kW CHP system.  Heat storage in a thermal store might be one way of getting around heat output intermittency.

You also have to look at your peak electrical load, before you design your battery bank and inverter system.  You should get about 5kW power from the 10/1, and you might have to run your larger appliances in sequence rather than all together.

Last winter I would start the Lister after breakfast, then start the dishwasher, and once it had completed its cycle start the washing machine.  These are all the sort of compromises you need to make when you want to go off grid.