Perhaps some type of economy can be set as well, making Trade agreements actually useful...
Say each clan starts with 5,000 yen/koku/gold, the Daimyo can 'buy' armor and weapons and such for his soldiers, so during Battles they can only use what they've bought, or the default gear.
With a map (like the one already posted) each province can 'earn' certain amount of cash for which ever clan holds it on a weekly basis (along with trade bonus, possibly building bonus as well).
If you guys want, I can write up some financial stuff...