Outdoor boilers are sweet but even pricier than a masonry stove. I like radiant heating, and outdoor boilers fit the bill. The biggest advantage I see with the outdoor boiler, is if you get a big enough one, heating a second or third building is as easy as running pipe.
As far as the stove being too big, there are many plans for many different needs. With good insulation and an open floor plan, it wouldn't take a big one. But it also fits the bill for an oven too, you can make it have more cookspace...You can get creative. You can even hire out the planning and the masonry work, even have prefabed units. When I buy, I'm putting one in, that or an outdoor boiler.
But yeah, a masonry stove with the flue backed up the the thermal mass of the greenhouse would probably work great as the grower would only have to fire it once or twice a day.
As far as trees...Thanks to the pine beetle your tax dollars fund the clearing of large swaths of forest which in turn are sold/given to businesses, like the pellet factory in Kremling, for refinement and resale to the taxpayer. Sure would be nice if they set up a few log depots instead. And if you can convince a person to let you do some fire mitigation, you don't even have to buy the permit and trek over the forest. Also lumber operations (which tend to be located near large forests) have plenty of 'scrap' that can also find it's uses in heating for cheap.
But I think one day a huge solar water heater with a giant phase change thermal mass might work well.