We could draw up a charter, have it notarized or whatever the local equivalent is, and stick it into a house of record. Being accepted as a mage-knight or whatnot would be pretty helpful here, it gives you something like a noble's station and privilege which allows for these sorts of enterprises.
The company will likely prosper well if it follows the structure of feudal enterprises lead by military nobles, meaning it lets people jump ranks in exchange for their involvement. Thus, joint-stock - the noble (you, the fake mage-knight) provides the cash, materials, and some of the expertise, and the workers, administrators, and foremen provide their own expertise and labor. Labor is as much stock as the implements used to do the job - you can't swing a pick without manpower. Therefore, it should be rewarded at some rate with company stock, which can be traded or managed for money and (probably) social status.
Thus, a worker at the company could elevate himself from a simple freedman to a middle-class man if he worked at your claimsites, and his interest in doing a good job would only grow with his stock.
You also pay these people a real wage, weekly. Whatever's reasonable.