Welcome to the forums HaloDS! Don't worry about not understanding everything, all this new information can be pretty daunting at first! You'll soon get the hang of it :]
Couple of tips with the Bondo: (And the Sticky, theres some great advice there:
http://405th.com/forums/index.php?showtopic=3711 )
So, be extra careful to measure out the right amount of hardener! The first time I used it, I mixed too much and it went hard in a matter of minutes - which was pretty useless! I sat there like, Facepalm! Just be sure to check the tin/tub to find out the ratio of filler to hardener ;]
Also, its a good idea to have several different sized spreaders, 'cause on certain armour pieces there are small details - these might be lost if you use too much filler or use a spreader that's too big. You can usually get packs with different sizes. :]
Good Luck! Hope everything goes well, drop me a PM if you get stuck or need any advice, I'd be willing to help :]
Oh! And love the idea of the silenced SMG, I'm sure it will be great