Bonjour,
I agree with what Oracionela offers. I will add to this, a creation of a GS / GM guild with a sufficiently low tax of 10-15% would be perhaps also interesting at the max level, as this we have access to the most requested buildings (altar, forge, farm in particular) and always at the highest level. The other guilds will be able to continue to climb their cities to reach the max level while continuing their achievements.
Thank you.
Laulau