I would like to implement a resource-bonus system similar to the corporation effect in BtS, for example giving silk +1 happy and +1 culture. Does anybody have any idea how I can start to do this?

One of my favorite aspects of the game is the modern-era corporation-powered resource gobbling, and I'd like an element of that in the ancient era as well.

You could try to convert them into guilds.

Other name, other symbol, other values...done.