Originally Kamael skills required souls to use, but since Gracia part 1 that requirement has been removed. Souls now increase the damage output of skills.
Your ranged skills get significantly better when you reach Arbalester. Twin Shot hurts quite a bit and Soul Shock is very useful for getting someone off you for a sec. Unfortunately the first class change doesn't really give you a good view of the capabilities of the class. Arbalesters are great at survival with the various traps and shots. Though unless you can afford decent equipment you may want to rely on your rapier till 40 or even into B grade as the cost will be less. By A grade levels you'll have enough mp to be able to hunt with skills quite a bit more, giving more time for mp herbs to drop.