Hey! I run Nightstalker pretty extensively so hopefully I can offer some help.
First, focus on Intellect and Strength. The NS grenades aren't fantastic, but the Smoke bombs are pretty incredible. I highly recommend the Sealed Ahamkara Grasps, though Graviton Forfeit will work as well if you're looking to capitalize on your mobility (not as necessary with this subclass, but that's my preference)
I primarily play PvE, so for my loadout, I use Vortex grenades. The Voidwall grenades are also very good, but they don't seem to deter stronger enemies in the same manner that the Vortex grenades do, and since the primary purpose of the NS grenades seems to be area control, I consider that pretty critical.
Beyond that, I use Triple Jump, Blood Bound, Envenomed, Lockdown, and Shadestep. The main tactic is to fire Shadowshot into a crowd of enemies, then to toss a smoke (or two, if using SAG, but I recommend holding onto the extra as a panic button) and let loose with your firearms. This deals pretty crazy damage to groups of enemies and is especially good for boss battles with lots of adds (Dust Palace, Undying Mind, and Sunless Cell especially come to mind). Shadestep is mostly there because it is the best option of the three, but it adds a nice quick escape option, especially since I tend to focus on Armor and Recovery over Agility for my NS. Obviously you can switch up the Shadowshot, Smoke, and First Column, since all the options are pretty viable. This build is very offensively-oriented and sacrifices some team synergy for raw power.
For primary weapons, I use either Ace of Spades (trash disposal), Smite of Merain w/ Firefly, Red Death, or occasionally a hand cannon that I got from an engram. In my secondary slot, I have either Invective, Jingukogo-D w/ Crowd Control and Feeding Frenzy, or 1000-Yard Stare. For heavy, either Sleeper Simulant (rarely) or one of the legendary or exotic swords. I recommend avoiding Void-type damage on your weapons since you'll have that from subclass abilities; the only exception is if you are using Zhalo Supercell in your primary.
For armor, try to find a chest piece that buffs armor for using a Void subclass. This will really help you tank damage, and its much more useful than any of the Recovery equivalents. For your helm, Hands On or Inverse Shadow are your best options, and Invigoration or Infusion are the best second-slot options. For the gauntlets, Fastball or Momentum Transfer are my preferences, and the second slot obviously depends on your weapon preference. Same for the boots, though Void Double Down is a definite pick, since it'll buff up your Agility. For reference, I use the Raid and Dead Orbit armor, but it doesn't really matter what you use specifically as long as you can get the perks.
Hope this helps!