So I should look for + lightning damage skills then?
Gearing process for shadow would be to first focus on getting a good weapon. With rares in every slot you'll have no problem killing everything for you 6pc(assuming it's your first char), at which point Impale will one shot everything up until like torment 10 even with rare gear/no skill/elemental damage, it's just that strong.
I'd highly recommend investing your first 25 death breaths into a dagger upgrade legendary cube recipe, as the only 2 daggers you can get are pretty good. I find Greenstone one to be better for farming low torments, so hopefully you get that one. Use the lightning FoK rune and just vault into a large pack of stuff and kill everything with it everytime it's up, while you Impale the elites and stuff.
Other good item for shadow is the vault belt. It's great for moving around, doing bounties and other stuff like that. It's like a poor man's Danetta set(but it doesn't waste your weapon slots), Impale, vault a bunch of times, Impale, vault a bunch of times. And then obviously you want a Dawn to cube for perma vengeance, and a Visage to go with it for the damage reduction. On most DH builds, these 2 take the weapon/armor slots of the cube.
Then really what you want to do is get 6pc UE with a Yang's Recurve and Deadman's quiver, so you can multishot farm, it's just way more efficient for torment farming. You can keep farming as Shadow, but it'll be slower. Shadow excels at more difficulty content(GR50+), especially in a group setting but the lack of aoe makes it so so for your basic farming. I've been climbing GRs with Shadow myself cause I find the playstyle interesting, pretty sure I'd have an easier time with Marauder or UE but it's just fun to see the big crits and chunk elites like they're low torment trash.