It's actually pretty hard to max out all your weapon skills. So far I've only gotten Hitman status with the Pistol, Micro SMG, SMG, Shotgun, AK-47 and M4. As for the Silenced Pistol, Desert Eagle, Stubby Shotgun and Shotgun, those are poor because I hardly ever use them.
It's okay though. All you'll need is the SMG and AK-47 or M4. Use the SMG for close targets and the M4 for longer range. Here's a good tip from someone who's captured all the territories. Usually your enemies will run down a sidewalk in a straight line, even with a bunch of them. So just stand on the sidewalk, line up your gun and pave them down with headshots.
There were numerous times where I eliminated everyone in the third wave with just a clip of M4 ammo.
Oh and don't worry about ammo. Just start capping with around 500-1000 of SMG and M4 ammo and you'll be fine. Don't even bother with going to AmmuNation, just take the ammo from the dead Ballas or Vagos. I easily got 5000 rounds of ammo just from capturing territories.