Some of that depends on the specific model, but;
Trigger: It's a shotgun, not a precision sniper firearm. Suggest you stick with the OEM parts. But that's just me.
Choke: For a defensive SG, stick with Cylinder or Improved Cylinder. But that's just me.
Red Dot Advantage: Both eyes open, focus on target, quicker shots on target. . Period. That's NOT just me. That's a RDS fact of life. There's a reason that competition shooters separate iron-sight classes from classes with RDS's.
Other bolt-ons: Sky's the limit, along with your wallet contents. Knock yourself out. Bolt release - Nordic (btjm). Safety - OEM (btjm). Charging handle - OEM
Other stuff - look around on the forum. Every doo-dad, trinket, bolt-on, screw-on, glue-on, etc., has been tried here. If I were building one, I'd think about a light. But that's just me. ?