Since you have to level up to earn a light or heavy body, I think you will start with 1 smg and 1 ar and have to earn the rest.........throught challenges
I doubt it. I think all but 5 or 6 weapons will be unlocked from the very beginning; maybe there's one gun missing from every category (sidearm, shotgun, assault rifle, smg, sniper, heavy weapon). There are only 4 challenges, which are broke up into three difficulties; furthermore, only the first two difficulties unlock things.
And they are not going to force you to play challenges to unlock weapons, it is only to unlock a few more options. They are optional, not necessary.
Edit: @ Riddike
Again, the majority of weapons will be unlocked from the beginning. Its not Call of Duty where you have one of every weapon type unlocked and have to unlock everything else. Weaponry options will be available from the get-go, so someone can jump into a game right away.