Outdoor wood boiler

Don't forget the incidental expenses-
A GOOD chainsaw, safety equipment and the ability to safely use it.
A good woodsplitter. I don't know about you, but I'm getting too old to swing an axe much anymore.
A healthy sized generator/inverter. If you're going to count on your woodburner(s) for heat, make sure you can keep the induction & circulation pumps operating in case of a power loss. The inverter or line filter makes the power "electronics-friendly", so it doesn't play havoc with any control boards, computers or other sensitive electronics in your home. That way you can stay on FABO. :)
I have a Central brand (forced air)- it' okay, but I sometimes wish it had a bigger firebox door. My brother in law has one that has a large door that he can load stumps/crotches and other big pieces into- very handy. I don't remember the brand offhand, but it's a closed system (not connected to home's potable water) and he runs an RV antifreeze mix in it. Heats his home and shop with it easily in northern Minnesota; land of the nine month winter...