If you want to give a knight less money, shrink their estate. Give them more money? Make their estate bigger. I don't see a need for all this complicating of things.
True, but with some regions, it is impossible to give everyone enough gold to meet the expenses imposed upon them with these means. There is simply not enough gold to go around. The accepted solution at this time is not: "Just field the largest unit you can with the gold you have." I am totally fine with such a solution and am generally avoid having any of my noble characters ask for money and instead field sub-optimal units. The solution I have seen most often is to create or designate a "money giving group" and then have the knights and lords that make little gold go asking for gold as needed. This is, in my opinion, not the kind of behavior I imagine the "highest of nobility" our characters are supposed to represent would engage in. Plus, it adds a lot of overhead.
Say there is a badlands region that only produces 50g per week for the lord (no knights). Then add on to the fact that the realms general has decided that every troop leader must field a 600CS unit (or a unit of such strength that the lord can not afford it). The duke, who wants very much his 15% share from the other, more profitable regions sets the tax to 15%. That leaves this lord with an income of 43g or so. What is the solution? The Lord must now go begging for grants from his liege, the ruler, the treasurer or some group of rich nobles who have been established to give handouts. Then the giver and taker of the money has to stop doing fun things like attacking evil outlanders and spend time at the bank making the transfers.
My proposed solution makes it possible for the duke to keep his 15% tax on the other regions (the ones that earn well) and then give that poor lord enough of a stipend to cover the expenses of a quality unit. Every tax day that lord simply gets enough income to cover his expenses. No need to go begging. No need for anyone to go spend more time at the bank.
Plus, it makes it possible for dukes to make certain regions more appealing to potential lords. Now: "Would someone like to be a lord of this poor rural? You will make much less that you did from your estate at the capital but if you are willing to go beg for gold from our generous welfare council, we will give you handouts as needed." With this proposed feature: "We need a lord for PoorRural. Any takers will receive 100% of PoorRural's tax income plus 50g per week."
The same scenario can be applied to knights. Say I have already given 2 knights 40% estates and end up taking on a 3rd knight. With this there may not be a need to change everyone's estate sizes and tax rates as you can simply choose to not tax the new knight and then give them a stipend. The new knight will not need to go begging and there needs to be less time spent at the bank. The lord, might even petition their duke to see if they would be willing to reduce their taxes or increase their stipend if the lord's income has dropped too much from taking on the new knight and ensuring that the knight has a reasonable income.
Plus, given a little time a realm will reach some kind of equilibrium. All knights will receive the estate size, tax rate and stipend amounts needed to cover reasonable expenses. Each Lord will have a tax rate or stipend that ensures they can cover their expenses - after all, it is possible that their duke is willing to adjust the lords loss of income incurred by taking on a new knight by adjusting that lords tax rate or stipend. The dukes do not usually have so many issues being short of money but it is still possible for the king to adjust tax rates or stipends to ensure that they all have what they need. All without nobles begging for money, the need for a welfare council and less time spent at the bank.
Regarding negative tax percentages, I find myself a bit skeptical. If we give a lord a negative 50% of the lords income and that lord loses a knight causing his income to raise from 70 gold to 100 gold, I will suddenly find myself paying the man 50g for a total of 150g instead of 35g for a total of 105g. I would be a little unhappy about that. Plus, this gives the lord one more reason why they should be careful or hesitant of taking on a knight. If doing so reduces the lords income their stipend from their duke is also suddenly lessened. Using a fixed amount eliminates this uncertainty and confusion. It just seems simpler to me.
As far as s simple interface goes, I think it would only take a minor adjustment to the GovernEstates page for lords or the equivalent for the dukes/kings. Just add a column for "tax rate/stipend" that lets you set the tax rate or stipend with a drop down menu per knight. The menu would contain a list of values like:
50% Tax
49% Tax
48% Tax
47% Tax
46% Tax
45% Tax
...
1% Tax
0% Tax
10g Stipend
20g Stipend
30g Stipend
40g Stipend
...
490g Stipend
500g Stipend
The lord/duke/kind simply selects a value for each vassal and that is all.
