In Anno1800, you know when upgrade is available and you know when you are able to upgrade.

But my question is: At what rate/percentage rate should you upgrade your residences? When the time comes to upgrade, how do you know how many residences to upgrade and how many to keep in the lower tier as "back up" residences for future lower tier jobs?

Let me give an example. You have 800 farmers and 1500 workers. You have come to the point where you have the ability and allowance to upgrade almost half of your workers immediately to artisans. How do you figure out how many workers to upgrade and how many to keep as extra for your future pig farms?

Thank you.