Well there are 4 classes, support, assault, engineer and recon.
Now support get ammo pack to rearm team mates, you also get to unlock a heavy machine gun, a shot gun, a gun turret and other fun things.
Assault get to play with assualt rifles, thealso get a medi hub thingy to heal your friends and can unlock a defrib and rifle rockets.
Recon get demo packs, anti personel mines, a sniper rifle and a turn invible thing.
Lastly engineers mainly blow up vehicles with motion mines, vehicle repair thingy, anti air rocket, guided missle aand an unguided hard hitting blow-the-crap-outta-tanks-in-one-hit thingy.
I hope my amazing guide has helped you lots into choosing your class

But either way, you get your unlocks pretty fast if you know what your doing so you can have unlocks in several classes, and also if you get NS then you get a free unlock with every NS award. Anyway hope to see you on 2142 soon
And in answer to the armour business is that you can chose before you spawn whether to wear light armour or heavy armour, heavy armour gives you more protection and light armour lets you sprint further but you might as well be wearing ntohing for all its worth as it offers no protection