for pictures it is a good idea to look at the cover of the Front Sight magazine, and take a look a Zack's set up, for a written suggestion...
I'm now shooting Steel Challeng with rimfire due to the primer shortage, but don't think it is a dead end... I shot PCC for about 5 years prior to Covid... bottom line is that it allows you to shoot your AR style rifle on a limited depth range typically pistol range, and on steel that the 9mm won't damage
for high end guns... some sort of delayed bolt, not that the JP with the silent adjustable buffer system is a slouch... MPX with a gas system... MP5, Angstadt, roller delayed...CMMG radial delayed (my PCC)....
for optics, I've become a Holosun fan boy with a H510c (I like the green circle dot reticle, but have a couple of red ones), with roll over point blank, not necessarily optic so you don't have to adjust for sight height above bore for close, precision head shots
carbon fiber, or aluminum shrouded barrels to help increase speed of transitions
good muzzle device, and hydraulic or tunable buffer system
ergometric fitting butt stock... I like a SOCOM cheek rest
high end trigger .. Geissele, Fast Fire etc
on the other hand ..., regular blow back, mid price trigger (I use a LaRue MBT) , good comp like a modified Miculek, hydraulic buffer like an Enidine, H510cg dot will allow you to tune your ammo, and get into the game, and let experiences lead you in what direction you like... regards Les L747