Actually, it's not so much the buying itself that could be automated, because as you say it is a complex process: how much to buy, where to buy from, the timing of the buying. However, the posting of buy and sell offers could easily be automated as it can be easily be fixed in advance (e.g. post a sell offer for 50 bushels at 20 gold every 7 days). The traders can handle the rest.
Yes, and as has been said many times, there is currently work to provide some sort of automatic system.
