Somewhat only I’m afraid, I haven’t gone around to testing different editors myself; I can only tell you of what I’ve heard and read around here. Qubicle constructor by Minddesk works, of course, but that’s pay to use, so if you’re not sure that you will be modelling a lot, nor have the money for it, it might be better for you to look at free alternatives. For those, there is Stonevox by @honestabelink, that one has pretty much what you need to make models just for Stonehearth. MagicaVoxel is also a popular, and free, editor but it can’t handle multiple matrices and therefore can’t really be used for models that play animations, such as doors.
For the tutorial itself, it’s pretty solid; there’s just a couple things I want to mention:
For point 7: there’s a comma there that shouldn’t exist. It gives a mean error in that the game doesn’t say there is a problem, but the building editor will be completely unusable as a result.
For recipes.json: when referring to the recipe’s file by starting with "file(../recipes/ ... )" is a bit unnecessary; the recipes file is inside the recipes folder to begin with. It’s enough (and cleaner imo) to keep it as "file(castle_door_recipe.json)".