I don't think I can address everything, but hopefully a few of my thoughts can help:

The first writing (which I'm aware of) is on tablets in the Middle East which were forms merchants or farmers used to track their goods, sales and incomes. So really the first Economy began where you'd most expect it - in the cities the goods and wares were dealt. In those days there were no nations or governments besides petty and tribal chiefs, who likely would have had their own equivalents of accountants to tabulate their expenses and crop production.

As the world got more developed, those in power and those dealing directly with the goods became more efficient in their ability to buy and sell to the best of their advantage. At the time Importing and Exporting would've been known as Trade. Such endeavors weren't reliable until the last few hundred years - but humanity has always been keen on Trading with their neighbors.