I strongly disagree. This seems valid and viable on the surface, but it pales in comparison to an Emerald for massive bonus critical hit damage.
For gems, I highly recommend an Emerald in the weapon, whatever gem provides you your primary stat in pants and chest (Emeralds for Dexterity on a Demon Hunter), and an appropriate helm gem depending on your needs (some builds necessitate cooldown reduction to be viable and require a Diamond, for example, while others benefit from additional tankiness via an Amethyst; some have no particular need, in which case a Ruby is probably your best bet to level faster).
All told, any class works and is fun (Demon Hunter is one of the strongest classes right now, FYI), but I advise against Witch Doctor as it’s a bit of a struggle-bus leveling up and it’s currently the weakest class in solo play.
Final tip: keep your follower geared (you’ll get one pretty quick and eventually have a few to choose from). Understand that they won’t do much damage, so utilize them for utility (select skills that cause roots/stuns/charms/etc. to make your fights easier). Itemization can do wonders in enhancing their viability as well (for example, a Wyrdward paired with a Thunderfury or Fulminator on the Templar to turn them into a stun-bot ;)).
Best of luck; hit us up if you run into any snags or have questions