Fixed bridle kites use 4 line handles (or bar) and you can't alter the amount of power whilst flying. Depower kites use a bar and you can de power whilst flying, this enables them to be used over a wider wind range than fixed bridles because you can change the amount of power accordingly. Depowers produce less power than the same sized fixed bridle, this is why people can fly bigger kites, also the power generated by bigger kites is useful for traction (for example it is easier to move on a board with a 10 metre than it is a with a 2m). Bigger kites tend to sit at the side of window once you are moving and pull without requiring constant input for the rider. With regard to larger kites, you will be able to handle the power, they move slower around the wind window and you won't be flying them across the middle of the power! (unless it all goes tits up!). I'm sure someone can do better at explaining if you have any more questions.
Welcome to the world of traction kiting! It's full of expense, frustration and dissapointment (when things break or the wind does not blow) but 1 good session makes up for it all. Have fun!