Currently it costs 4x as much to build a unit or building which I feel is fair, as your income theoretically also is multiplied by 4 (per year). Yet do all the changes of the mod also affect the AI? I get flooded with monstrous armies I simply cannot repel, even in the early game.

Unit Upkeep on the other hand is said to be increased by 50%. I don't see the reason for that as it as massive increase and imbalance to the vanilla feeling. You already pay 4x the price for raising troops which balances that you get 4 times the income per year but practically you also pay 4 times the upkeep now even per year. With 50% extra upkeep on top of it, it even stacks to 6 times. I feel this is a major factor that needs balancing that you don't get too much money but also don't get sucked dry by your legions.

Then "Agent experience required for each rank x 4, Generals x 3". While it makes somewhat sense not to get super agents/generals too soon, you will run into 2 problems:
A) The agents abilities still cost 100%. To reach the same experience as in Vanilla for a single action, you would have to do 4 times as much missions therefor yet since the prices have not changed it will also cost your treasure 4x as much to reach that experience. Therefor the costs here should be made much smaller (like divided by 3 or 4).
B) You will need 3 times the battles to upgrade your general. Yet you don't have 3 times as many battles in this game, leaving you at a disadvantage because usually the game expected your legions to raise in abilities more quickly.