Different ways to become shogun in Shogun 2 Total War

Asked 2 weeks ago and if no-one has further information will accept this as the answer:

From browsing forums it seem there is a hard-limit of 5 agents of any type, regardless of how many chains you have. You can never have more than 5 Metsuke, 5 Ninjas, 5 Monks, etc. http://forums.totalwar.org/vb/showthread.php?134068-Where-to-build-markets-only-in-fertile-lands/page2

The advantage is actually not that great. If you play a lot you do get more retainers and more experience for your general but it's overall strategy and tactics that will win you the game. My general currently has 8 stars and I remember when I started off I beat a 7 star general without using any veteran units or retainers.

As to how the players are matched, if you let the game manage it, it will try to find a player of your level if one is available, if not, it will keep searching for any available player of sufficiently close rank.