With early access I've gotten artiface up to 172 as of yesterday before the server shutdown. I have listed a few "test" items on the GTN, both looted (greens) and crafted (mainly mods/hilts/shields)
I think it's too early to expect much of a market. I imagine there are a LOT of people new to MMO's with this game who may not even know about the GTN and player crafting, existing solely on loot and vendor purchases.
The ONLY thing that caught me off guard, at first, was seeing orange items on a vendor. I had (mistakingly) thought orange items were ONLY player made items.
The biggest hurdle is going to be pricing for the craftables. You get the default listing price that the GTN sets for your item, but that may not be the going rate. You can also make level 7 items, but most level 7 players won't know they can even get to the GTN before their class quest takes them off their starting world. So crafting those, other than for XP and Reverse Engineering, isn't going to be very useful for the first couple weeks or month...until people get the hang of the game.