I didn't realize how "active" the forums were, so I'll start answering my own question since it's had a lot of views in hopes that it can help someone else...
TL;DR: If you're using Whirlwind, you must duel-wield! Changed Nerves of Steel with Brawler, and Superstition with Animosity. Aim for the Wrath of the Wastes gear set for WW build, as well as the Bul-Kathos 1H weapons set. Mantle of Channeling is great for Kanai's Cube.
One thing that I've found that is absolutely necessary for this build (because of Whirlwind) is that you NEED to be duel-wielding. Without it, you will constantly run out of Fury. In addition to the increased DPS, it also greatly improved my survivability since I was hitting twice as much. As a result, I replaced Nerves of Steel with Brawler since I'm almost always in the middle of a groups of mobs at any given time. It's pretty much a constant +20% dmg boost. Superstition, too, was unnecessary and very lackluster, so I replaced it with Animosity.
For gear, you'll want to aim for the Wrath of the Wastes gear set. It GREATLY increases both your rend and whirlwind damage; you can literally rend-and-run while sprinkling in some WWs as you move through the mobs. Weapons, you want the Bul-Kathos 1H set. It increases your WW dmg & movement speed by another 30%, AND it increases your Fury generation, which works beautifully in sync with Animosity. Don't forget to socket those puppies with the highest level emeralds you can craft, too.
In Kanai's cube, I'm using Mantle of Channeling. It increases your overall dmg by 25% and it reduces your dmg taken by 25%. I'm using Ring of Grandeur and Stalgard's Decimator in the other slots. The weapon is a nice damage boost, and I need the ring because I only have 3 pieces of the Wastes set so far. Your mileage may vary.
Don't forget you can upgrade your rares to legendary or set status in the cube, too. I got my first pieces quickly by spending blood shards on gear and then upgrading the rares. I've obtained 3 or 4 pieces this way so far.
I am by no means an expert, and there's probably better builds out there, but I was unable to find any. So take what I say with a grain of salt, try it out for yourself, tweak it as you see fit, and maybe you'll find what's perfect for you.
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I didn't realize how "active" the forums were, so I'll start answering my own question since it's had a lot of views in hopes that it can help someone else...
I copied the beginner build from icy-veins, and that is a good start I think. The page is here: http://www.icy-veins.com/d3/barbarian-leveling-and-fresh-70-guide-patch-2-4-3-season-9
TL;DR: If you're using Whirlwind, you must duel-wield! Changed Nerves of Steel with Brawler, and Superstition with Animosity. Aim for the Wrath of the Wastes gear set for WW build, as well as the Bul-Kathos 1H weapons set. Mantle of Channeling is great for Kanai's Cube.
One thing that I've found that is absolutely necessary for this build (because of Whirlwind) is that you NEED to be duel-wielding. Without it, you will constantly run out of Fury. In addition to the increased DPS, it also greatly improved my survivability since I was hitting twice as much. As a result, I replaced Nerves of Steel with Brawler since I'm almost always in the middle of a groups of mobs at any given time. It's pretty much a constant +20% dmg boost. Superstition, too, was unnecessary and very lackluster, so I replaced it with Animosity.
For gear, you'll want to aim for the Wrath of the Wastes gear set. It GREATLY increases both your rend and whirlwind damage; you can literally rend-and-run while sprinkling in some WWs as you move through the mobs. Weapons, you want the Bul-Kathos 1H set. It increases your WW dmg & movement speed by another 30%, AND it increases your Fury generation, which works beautifully in sync with Animosity. Don't forget to socket those puppies with the highest level emeralds you can craft, too.
In Kanai's cube, I'm using Mantle of Channeling. It increases your overall dmg by 25% and it reduces your dmg taken by 25%. I'm using Ring of Grandeur and Stalgard's Decimator in the other slots. The weapon is a nice damage boost, and I need the ring because I only have 3 pieces of the Wastes set so far. Your mileage may vary.
Don't forget you can upgrade your rares to legendary or set status in the cube, too. I got my first pieces quickly by spending blood shards on gear and then upgrading the rares. I've obtained 3 or 4 pieces this way so far.
I am by no means an expert, and there's probably better builds out there, but I was unable to find any. So take what I say with a grain of salt, try it out for yourself, tweak it as you see fit, and maybe you'll find what's perfect for you.
Cheers!