um, not to sound like an ass, but the plaza should be PACKED with NPC\'s right now. They should be trading corn, rice, eggs, rugs, carp fish, (oh and friggin\' apples) etc. It should be hard to get through them. Right now this is a world catering to Adventurers. There are very few, if any \"normal folk\".
Anyway, one NPC guild tresurer/banker would be fine too. And you\'re right, I have no idea how many guilds there are.