Buy the basic Merchant skill as soon as you can, it saves you quite a lot, but don't put any skill points into it immediately. Master Merchant is worth getting eventually IMO, but not until you've got your main weapon, armour, and magic skills up to expert, and water up to level 10, so that you can get GM as soon as you can make your way to the GM trainer. [You can do this at a fairly low level if you know exactly where you're going; you get Town Portal and Lloyd's Beacon before starting the process, and then just run like blazes, avoid battle, get the promo, and Portal out. Then go back and clear the place out when you're stronger.]
I would also recommend daggers rather than staff.