Bob: I don't have much experience in heating but here's my 2 cent's worth. Any system you choose should take into consideration the amount of time it takes to recover the savings as compares too other methods. Wood is great, and cheap, but requires your attention frequently. Natural gas or propane are reliable, but not necessarily cheap.
A friend of mine has a mechanics shop with 13 bays and a parts store in the middle. In each of the wings he installed a "used oil" furnace. The cost was near $ 4000.00 ea. The good thing is that due to his business, he has 'free fuel', maintenance is very low, and the tank holds enough to last several days.
I don't know what the situation is where you live but, where I live, most garages are happy to give you the used oil. I have read that you have several pieces of equipment, so I assume that you have a truck large enough to haul in what you need.
I do like your idea of having a combination of systems to heat this area. As I said, I don't know that much about the subject but I do enjoy these types of discussions. Have a good one ~ shao
Measure twice ~ Cut once.
" The most certain way to assure total victory is to understand that anything less, is a defeat."