With a 7-10 lb trigger pull a metal trigger does much to improve the trigger w/ no effect on the actual mechanical functions of the gun. Can't imagine that it would be a problem.
Can't reiterate enough the dust cover. Trigger guard locks it in just like it locks in the barrel. Here:
https://www.keltecweapons.com/dust-cover-451 Reduces potential to get stuff into the barrel and into the bolt/bolt tube.
Sub2ks -- really the easiest fix for most folks' self defense use at self defense ranges would be a dual weapon light and laser. If mounting sight options to your HG, I'd recommend installing rail stabilizers that bolt to barrel and interface w/ HG to ensure repeatability.
One benefit of offset is that it pivots the charging handle away from your body and anything likely to tangle it, but also make bird winging more likely, which isn't preferable when working corners. But I think you need to mount a rail and mount an offset to that in order to have folding clearance, which moves it more off the bore than you might like, potentially affecting cheekweld..
Don't get me wrong, I like the Sub2k, especially for what it is, but it's REALLY easy to spend $150-300 on prudent upgrades on the gun, with the lower # being upgrades I'd consider essential for fighting weapon. Vs the new Ruger PC9 carbine, I'm having an increasingly difficult time justifying the Sub2k over that gun, especially for rifle only shooters shooting that and perhaps a ruger 10/22... When considering upgrade cost, the Ruger comes out at least $100 and up to $250 less in accessories and considering usual $75-100 price difference vs sub2k, that's an even price to $150+ cost savings going the ruger route. Definitely food for thought. Sub2k is faster to deploy, more compact, typically lighter, and better for one handed control and firing.
Definitely try the two finger changer handle, if you're skipping the heavy. Makes a major difference. I tried the poly cover for standard charging handle and it only succeeded in pinching my finger. Insofar as heavy charging handle, many 9mm Sub2k shooters have transitioned to heavy .40 buffer w/ no issues, which should suggest margin to transfer to heavy charging handle. And if it doesn't work, it's a 1 minute part swap. Effectively, I think it's fair to say factory spec is equivalent to AR w/ carbine buffer and standard spring, whereas upgrades can get you to AR equivalent of H1 buffer (if midlength, or H2 or H3 if carbine). Especially if all your duty ammo is +p/equivalent, you should be golden (I think recoil springs are same across both calibers, but might want to verify).