Kobold trader DO bring wagons. And around a 6X21 area is needed for the basic 3x3 workshops[Butcher, Tanner, Kitchen, Craftsbold, Leather Works and Kiln], advanced 3x5 workshops[Leather Trimmer, Wood Processor, Sawmill and Bone Chipper] and industry 5x5 workshops[Leather Upholstry and Boneyard]. Farm plots, food stockpiles/pastures and dormitories enlarge this, so lets say 10x21 total, until you can get food moved underground. 8+8+21+21= 28 planks[7 logs worth of planks] for a full enclosure of the starting area. Cobaltpacked uses 20x20, because I included metalsmithing, tailoring and more advanced workshops[18+18+20+20 = 76 planks = 19 logs worth]. So with ~20 logs for the workshops, that means 40 logs to make a fully functional above ground kobold fort and ~25 to make a more minimalistic model. I usually get that done by the end of the first spring, midsummer at latest. And then you only have to do minor additions, which are much less of a hassle.
Tips to get this done as quickly and efficiently as possible: Bring 20 jack rats of either gender and almost immediately start butchering all but one of the male rats for leather for tents and meat. I usually go with a woodcutter, a carpenter, a farmer, a butcher/tanner, a cook, a leatherworker and a bone carver as my starting seven and enable carpentry on all of them at first to get the walls built quicker. Gathering clay boulders for building materials helps significantly.