It's mostly a source of error issue. If everything works out fine, that's great, but if there ends up being an issue, isolating the causal mechanic would get much more difficult.
Anytime any major project goes live there are always hiccups, thus one should be brought up and stabilized and then the other brought up. IMO, the New Economy does much more for traders then markets do, so I'd bring that up first and see how it shakes down for a month or so before even considering bringing something else live. I suspect the New Economy would bring more to the trader game then the Tourneys as well as having more overflow into general conflict-causing.
As trader, Ivote for new economy first. I would prefer to carry food in one direction, and return with steel in the other, rather than carrying 400 gold with me halfway across the map, only to have it stolen.
