Barrel length & Suppressor?

Barrel length & Suppressor?

Ok given Im still under age and have no use for these things, I still plan to get them regardless, in a few years.
Advanced-Armament's spr/m4 supressor http://www.advanced-armament.com/flyers/m41000.pdf what ya'll think?
and what barrel length should I get a 10'', or the 12'' thats out now?

As an excuse, well it would be great not to have to worry about hearing protection & also a 10'' barrel and folded stock, well I could drop it in the floor board of a car. Should I move to a city, well it'll be an excellent home defense wepon, but in all reality Id still probly prefer my P99 for in a house... but still these thoughts are all of an ignorant & nieve kid, when Im old enough I'll get the training and classes I need. What do you people think? expensive, waste of money?
Any one with a better suppressor-barrel combo idea please let me know, also I was reading on this sight but cant find it it talks about its silencer & its reliebility and how they shoot the barrel white hot it ruined the barrel but left the silencer fine and the same one is also supposed to boosta tiny bit of extra volocity not like a longer barrel, but still just a little, maby one of you knows what Im talking about... sorry for the long post feed backs appreciated ;D