i am a newb around here.
but i wanted to say something.
since you are going to focus on the economic aspects of the game, here is suggestion regarding trade. and its prices.
you can set up some base prices of the commodities viz Iron ores being cheaper than Swords etc. Now, when some one has to buy that, the prices paid will be decided based on the availability in the entire worlds market. If no one is offering, the costs can be the base price (or lets say 150% of the base price). The prices would go down with more offers in the market.
This would be pretty good in a MMO kind of scenario....