The actual requirements in vanilla are proud + 5000 prestige, ambitious + 5000 prestige, 70 holdings and 4 duchies, or 15000 prestige, on top of the requirement of 3 duchies or 35 holdings, 1000 prestige, and 300 gold to use the decision to found a kingdom. For a custom empire, the AI needs to be ambitious/proud and have 40000 prestige, or 120000 if they have neither trait in order for them to even have the option. In either case, the AI needs five (with proud or ambitious) or fifteen (if they have neither trait) times as much prestige to use each decision to become available in vanilla as the player needs in order to use the decision.