You can level up to 300 without making a choice at all, but you are offered a choice at 225 (I think? Might be 200). At that point, your trainer will offer to send you to one of two other trainers, who will offer you a quest which when completed locks you into that path, either weaponsmith or armorsmith. As a weaponsmith, you can go on to specialize as an Axesmith, Swordsmith, or Hammersmith. Each specialization has recipes available which can only be used by that specialization. Clicking "Trade Skills - by Trade" on the search panel to the left will give you the complete list of recipes, broken down by specialization. You might want to check the availability of the plans as well - some are only available in Instance runs, others only as world drops, while only a few of the higher level plans can be purchased.
I can't give any advice on the moneymaking aspect of the specializations - I haven't had the patience to make money off of anything yet.