I've got two 250 gallon propane tanks in my yard. One goes to my whole house generator which can go several days if needed; the other goes to the stove, water heater, and fireplace; this lasts several months, but not a whole year. After a few years experience, the best plan seems to be fill in september/october and again when prices come down in the spring. I'd probably try to get a bigger tank or a second tank for the house if we ever need to do meaningful work on the system, so we can fill once a year in the summer. Combining the two tanks I have now would probably be too expensive, and a dedicated supply for the generator seems good operationaly. The previous owner leased the tanks, and we kept going with that; it's probably better to own them as then you can get better fuel pricing.