I have no personal experience with what the round in question, but I have access to internet search engines and many years of experience and experimentation with firearms and cartridges.
For indoor HD, I think a PCC, and specifically the sub2k, makes huge sense, It's more accurate due to the 3 points of contact, and more powerful due to the longer barrel. In the many thousands of rounds I've put through mine I've had exactly zero malfunctions. Aluminum cased ammo not so much
, but other sub2ks handle aluminum case ammo fine. I wouldn't hesitate to trust my life to my sub2k. I think you made an excellent choice so relax on that consideration. (More on this all the way at the end)
9mm+p increases the pressure of the round from 36k psi to over 38k psi (10%). But 9mm has always been a fairly high intensity cartridge and 36k psi in an unlocked breech gun isn't something to take lightly. The .40 S&W operates at just shy of 33k psi. It might not seem to be much of a difference but in wear and tear on the gun it can be. If the breech opens too soon the danger of pressure will be immediately apparent. What can be done to help the gun better tolerate higher pressure ammo is to increase the poundage of the recoil spring and/or increase the mass of the bolt, both act to retard the opening of the action somewhat. KT doesn't offer a higher rate spring, but they do offer a bolt weight with more mass, or at least they did a few years ago. I think it costs $40ish. I put one in mine almost immediately because a more massive bolt gives more "oomph", to use a technical term, for feeding, but it also resists the bolt opening a hair longer to allow the pressure to drop before the bolt opens. I thought it might affect the operation of my gun and my use of minimum power factor loads (butterfly fart loads) that I use in competition, but it never did in a negative way. For me and based on my experience with the heavy bolt weight the replacement of the factory bolt weight is a no brainer. KT should just automatically replace it and make it the stock bolt weight IMO. (Maybe the heavy bolt weight is responsible for the malfunctions with aluminum cased ammo? IDK)
I still wouldn't feed the gun a normal diet of +p ammo even with the heavier bolt weight, but sight it in and practice with ball, then make sure it works with your HD ammo and is close to being sighted in with the good stuff. Close is probably good enough due to the distance involved indoors. But frankly, for HD, if you're doing it right you don't need +p. One doesn't fire, stop, and look for effect. In practice one fires until the threat stops or until you run out of ammo. You train to that end. What constitutes an end to the threat? The person leaving, attempting to leave, or falling to the ground, maybe some others I haven't mentioned. Now if it was to be a defense weapon outside the home the range can be longer and one would sight it in at that range with the more critical ammo, the practice ammo would take a backseat. But indoor short ranges? Close is good enough as long as it's close to the practice ammo.
Again, check gel tests for the round in question. But gel isn't flesh and the relationship in gel isn't a 1:1 relationship to flesh. But for good penetration in flesh you want about 14" in gelatin. Personally I would stick with what the LEOs use in theirs. That gives your ammo credibility and in no way can the DA attack you if it comes down to court. I use part of an overrun of ammo made for the federal go'vermin. It's standard pressure 148 grain HP*. But I can tell you what NOT to use. That would be any ball or FMJ ammo. It would be exactly the wrong stuff to use. It will give terrible terminal performance on target and zip right through to do damage beyond the target. You are responsible for every round fired and "whoops" doesn't begin to make up for harming or killing others. It's been stated before, there is a lawyer attached to every bullet, and that's not a fable.
*I use it for other reasons as well. It's inherently subsonic for use with a silencer should I need to use it indoors.
I think you might be on the right track with lightweight bullets and reduced barrier penetration in wallboard and 2x4 with the 9mm but IDK. But do your research, youtube gel tests would be your friend here to see how they actually perform. But I've found that in general, velocity really makes bullets zip through things while reducing depth of penetration. Yeah, I know that sounds like a contradiction. A lightweight 25 grain .17 Rem bullet @ 4060 fps does a remarkable job of going through 1/4" mild plate steel and one would never think so when handling the bullet (projectile) that resembles a needle more than a bullet. But that bullet totally tears itself apart and is spent. That's common for high velocity bullets. Slow and heavy bullets tend to stay together and penetrate deeply. The key is to hit your target and allow it to trap the bullet. Don't fire to warn or shoot wildly out of fear, and don't miss. Again, this is learned, as much as possible, with training. I consider USPSA competition to be a training ground. Maybe not so good for tactics because it is a game, but for training one how to deal with pressure and the stress that produces. Don't forget professional training and get that before learning bad habits that will need to be unlearned.
The screws make no difference since the items they screw into are embedded in plastic and the plastic does the actual holding of the moving parts in the proper relatioship in the frame. But change them if you want, it will make no difference to what you ask either positively or negatively. To state it another way the screws just hold the clamshell halves together and are under no appreciable strain. I know there are some folks who think the 9mm is a horrific round for recoil and stress, but it's barely out of the mouse cartridge category. Too, when it's fired the barrel and bolt contain the vast majority of what's happening. Everything you feel going on is minor in comparison to what happens a nanosecond after busting the primer. The majority of what is seen as being "the gun" is just a jig that the parts move around in. "The gun" is just a jig that holds those parts in a proper relationship for cycle after cycle.
Modern firearms don't get much simpler than the sub2k. At the first match with mine and after folks could see just how accurate and reliable it was, a shooting buddy commented, "It's really just a stick isn't it?". That was no lie. It's basically an upgraded early closed bolt submachinegun with a disconnector to make it semi-auto only. It doesn't get simpler or more reliable than that.
Links:
https://en.wikipedia.org/wiki/Overpressure_ammunition
https://en.wikipedia.org/wiki/.40_S&W
Can one do better than a sub2K? I think so. But it's expensive and it can't be half done IMO; it's either 100% or forget it. If you can't have a silencer that makes it a non-starter. I think a rifle firing the .223/5.56 WITH silencer attached is pretty much the best it gets for indoor HD. But it must be with a silencer. Don't even think of touching off either of these 55k - 65k psi rounds indoors without one if you value your ears. A silencer/suppressor/can doesn't silence the gun, there will still be plenty of noise, but it gets rid of the blast from the pressure of the round and that's what does the damage to the ears and makes one wish the round had never been touched off. I think this larger and heavier gun makes even more sense if ones plan is to stay in a safe room, and that doesn't mean an indoor hardened bunker or what's seen in movies. Contact a professional to get the lowdown on a safe room. Maybe the internet helps here? IDK.