1. Find the section in campaign_script called "G5 Faction Economy Script" and delete that entire section to get rid of giving or taking away money to AI factions based on their treasury.
2. King's purse is defined in descr_strat. Not campaign_script. For example,
The "denari" line is how much money Denmark starts out with. The "denari_kings_purse" is their king's purse.
3. Yes, starting faction relations are defined in descr_strat. However, if you actually want to change diplomacy, descr_faction_standing is the correct place to do it. Descr_strat can only change starting diplomacy, while descr_faction_standing impacts diplomacy throughout the campaign. Here is the part of descr_faction_standing that defines the relation change of factions with other faction's of the same religion.
Increase the 0.8 anywhere up to 1.0 and decrease the 100 if you want to make factions of the same religion like each other more.
4. I mentioned how to get rid of the artificial modifications of treasuries in point 1. However, there are also many, many economic and other bonuses that the AI receives in EDB. If you want to get rid of those, go to campaign_script and find the section called "Is the AI?".
Change two of the 1's to 0's. I've bolded them below.