Maracaibo
When I invest in a prestige building, does the figure come from my own supply or the general supply?
From your own supply (the figures you have earned), not the general supply. If all your figures are on the board you cannot invest, and there is no way to take back or fire an assistant. Spent figures return to the general supply. The English wording mentioning the supply was loose; the designer confirmed your supply is the right reading.