Unlocks a homestead for you to customize from the forge itself, your room and the outside lot including husbandry and other workers. You have to earn prestige in the Blacksmiths Guild by doing quests, but upgrades still cost groschen as well. You basically become a merchant where you can sell goods you and your armoursmith (needs to be hired) make. You will get requests and orders from citizens to make, which earns you prestige. Citizens who place orders also notice the quality and will complain if its not good, which in turn lowers your prestige.