I have had a chance to get caught up on this one.
Hand fire furnace get the one you will be most comfortable with. I'm with Doug with the Clayton. If you intend on being around to keep it going every 12 hours or so. It gives you the reason to be in the shop at least. Stoker All I know is what I've read here and since I have a clayton it might just get stoked in the off season. Unless I find a big boiler to do both buildings.
Ruling on in shop solid fuel open to area as I know it call for 18 off the floor to bottom of firebox/ashpan opening.
Remembering draft is pulling. Gas vapor from gasoline,acetoline,mapp,beer
or propane and so on are also concerns to the insurance industry.
Furnace rooms; weatherstripped door, sealed room design with rated walls,fresh air intake for combustion and furnace return air from ceiling. Feeds can go to the 18 off floor ruling. With no wall penetrations below 18 inches including outlets inside or outside of enclosure. Another words you would have to be an idiot to open the door to this room with gas vapors at your heals.
All in all we can build it to a safty level but the Ins Co will not have to insure it if they so choose.