I didn't really start picking up significant upgrades in gear until the very end of Act III on NM and am still wearing a lot of level 20-25 items simply because the stats are better. I know that I started Act III at around 6k HP and after killing Azmodan I was level 48 at about 13k HP and 2.7k DPS. It's hard to give advice for gear other than "be luckier" but it may be worth looking on the AH to see if you can find a weapon that falls within your price range that is a significant upgrade. Barring that, you could try a few more runs through Act II although I'm not certain which quests would be choicest for gear farming.
In terms of your build, I'm really surprised that you have no snare of any kind. Kiting is the only way to survive and kill most Champion/Unique encounters and a snare goes a LONG way towards that. It may be worth swapping Bola Shot out for Entangling Shot + Chain Gang instead. Plus it will make it much easier to maintain distance for Steady Aim.
Also although I was an avowed Multishot user all the way through Act I NM, I realized it wasn't cutting it in Act II and switched over to Elemental Arrow + Ball Lightning and the difference was huge. At first I didn't like it because of its slow speed and comparatively narrow area of effect, but I realized that I was doing so much kiting that all the enemies were lining up naturally. With its drastically superior range (it travels about 1.5 screens whereas Multishot seems to not even extend a full screen away), low Hatred cost making it incredibly spammable, and ability to hit most enemies twice if they're snared, it ended up being a significant improvement.
If you're looking for more Hatred you can try subbing in Companion + Bat for Preparation + Punishment. I can understand the desire for the big chunk of Hatred, especially if you're burning it all on Multishot spam, but the way it interacts with your escape abilities makes it a bit counter-intuitive. You're going to be popping Preparation on harder enemies that you need more Hatred for, but for those harder enemies you're going to want to save your Discipline to spend on your escape abilities. With the Companion while the Hatred trickle is more gradual, it allows you to save your Discipline for when you really need it.
Under my current build I've only died twice. Once was to significant computer lag and once was to being pinned in a corner of a tiny single-room dungeon by an Arcane Enchanted Waller. Otherwise I've had no problem. Here's the build for reference:http://us.battle.net/d3/en/calculator/demon-hunter#bRcdjT!Yce!aabbYZ
stack more vitality and change the preparation to the healing one, you can drop vault, i can't think of a time that smoke screen isn't better to use than it
I've never used Smoke Screen, but I use Tumble all the time to avoid targeted effects like the ones Frozen and Mortar mobs have and the attacks of most bosses. I'm assuming Smoke Screen doesn't make you invulnerable to these effects.