since u have metal in your body, whatever branch u join with, at MEPS (Military Entrance Processing Station) I would not bring it up at all.....if the doctors find out they could discharge you immediately.....
boot camp is nothing more than a big game.....all the drill sergeants and drill instructors do is test you.....see how much you can take, handle, what is your breaking point.....once they find out that you dont have 1, and you actually follow instructions and do as your told, it gets a lot easier.....
always remember to stay positive and clear headed......never in my life did I think I would join the military and be able to even think about boot camp.....but I did, and I gotta say, it was worth it....
you just have to decide what branch u wanna join.....look at the benefits they offer, school, etc.....see which branch would fit for you and go with it.....
if you need anything else man, let me know, Ill try to answer any other questions u might have.....