1. Download DnSpy
2. Open Taleworlds.CampaignSystem.dll
View > AssemblyExplorer (so the code on the right side opens)
Scroll down to Taleworlds.CampaignSystem.SandBox.GameComponents > DefaultSettlementTaxModel
Change the tax in CalculateDailyTax, for example to 0,5 - this would mean 5,000 denars instead of 3,500 in a town with 10k prosperity. You can also change GetTownTaxRatio and GetVillageTaxRatio, I think that`s the taxes that you get by villager parties and caravans.
In DefaultSettlementProsperityModel you can change the growth rate of hearths and settlement prosperity and up to which value it grows at which rate.