Don't forget to look into a reinforced bolt handle. If you don't learn how to cycle the bolt correctly, with your thumb behind the nut that holds the handle onto the bolt,you will end up snapping it off. I would reccomend using a heavier weight BB, at least a .36g or better yet, a .43g. This decreases the FPS, but allows for greater accuracy. The nozzle can be taken off with a crescent wrench, no problem. Like everyone else says, a correct spring guide and piston for your spring is essential.
Good luck.