| Warwynd |
Here's My thoughts on this if you are even still looking at this post.
First off the idea of forming fiefs within your land is a good idea for exactly the same reasons it was done in the real world. It makes it easier for you, the king, to administer growing territories. I think that the control DC should still be based on the kingdom as a whole unless you are planning on running each of the smaller fiefs as separate nations, (ie. separate kingdom sheets). In that case then perhaps that is a good idea to alter control DCs. But it has been my experience that once the kingdom gets going that they will have little difficulty in making those rolls. In my Kingdom only a one fails on any given check, even with a -20 penalty applied.
On the issue of taxes; in the real world feudal system it was standard that a vassal state (Barony, County, Duchy, etc...) paid one fifth to the liege lord (20% taxes). This took several forms. It wasn't all paid as wagon loads of gold coin shipped to the capitol every month. Rather it took the form of services, raw and worked goods, food and livestock, and troops. In peacetime they were to maintain a militia and in times of war they were often called upon to send even more troops to support the war effort and often their own services.
As far as trade between fiefs that would almost certainly have to be decided by the individual rules of said fiefs, but, I suspect that their will form a standard economy in your campaign if you decide to go that route. The concept of KISS should be observed here unless you really like getting into realistic simulations of macro and micro economics. I enjoy a good deal of detail myself but that threatens to cross into the realm of tedium. I would avoid overly complicated systems and try to come up with a workable structure kind of like what you suggested.
The idea that the Liege send BPs to help out the vassals makes perfect sense as well. It was in fact the duty of the Liege to support the vassals as much as it was their duty to support their Liege.
I realize this is long after you posted it. I just found it minutes ago myself, buried as it was, in the Kingmaker forums. I hope this is still of some use to you and good luck with your Kingmaker campaign.