I think ItemExchange has what you need. You'll have to restock the chests thou.
Villager trading is disabled but I've seen plenty of shop builds that use villagers as decoration.
As for spawn towns, thats a little tougher. Spawning on the server happens close to origin, which is out of the way for most of Chanada/HKE. You'll be in the heat of plebbit country. You'll also end up with more griefers, as they'll spawn in close to your city.
I'm not bashing your idea, I'm just letting you know it'll be quite the task on this server. If you want a sand merchant hmu