what gun are you considering?
a new breech is usually just to get a different color for show, but you can also get one that has different threading to allow for say, cocker barrel threads
firing cans dont do that much and are usually for show through cut through bodies
(it is said that they increase efficiency a little bit though)
for the picture, you need a 50 pixelx 50 pixel picture then go under account setup i think it is, or something like that and upload it (i think, not positive, havent done it yet)