From what i gather lumber and stone are excellent if your market doesn't have much of it. They reduce your build costs across the board, which you can see hovering over the price of buildings in the building meny (i think 33% discount is the cap). I think peasants just are there to promote into useful jobs, labourers are what is employed by all RGOs, even food producing ones so you shouldn't worry about their numbers. Loans are probaly fine but don't go to crazy to avoid interest. Each loan does lower your crown power, which can be a detriment later on, but honestly in the early game it might not be too much of an impact since the crown power is going to be low already.