I've seen a lot of nice suggestions/comments, on differents matters, here.

What I would add, then, should be a "depth level setting" for all fields of the game (trade, agents, battle orders types), so that the battlers would have very complete and realistic battles with loads of things to manage, while the trade would be some "yes/no", the unit master could use a very detailed unit development "tree" and artisan tree so that he could desing his units completely (armors, weapons, type of training, type of mounts, etc...), and so on...