I would go for it if you have a drain in the room, The Furnace is a 80%, so it is a little old, I would check a few things first. It is a large outlay of money at once. How long do you expect to live there, Is there a wall you can vent the tankless out of? If you get a HE tankless where there is an inlet and outlet pvc vents you do not need to concern about hot exhaust gases. Since you do not have ducts to move around the heat you must use multi indoor units and may get hot and cold spots. Your ductless must be a heat pump you will need more electrical power and as I said a drain for your washer and more electrical power for the dryer. This would cost you around 20 k to do this which you may only half back when you sell. To get your money back in saving may take 20 years.