Ask and you shall receive!
Although I can’t answer whether or not you can leave gaps where doors should go, I would imagine so … a no door option for customisation, or something like that!
As for number 2, I would imagine they would have a similar construction mechanism to buildings, or at least it would be smart to include a procedure similar to buildings for fencing off larger areas, your guys then simply put the fences up when you’ve crafted the fences.