There's no real reason to install the shims to eliminate the firing pin lock parts unless you want to just because. You can get a good trigger either way...eliminating those parts makes it a bit easier but that's all. I have Series 80 pistols with excellent triggers and one I purchased that already has the shims installed...also a great trigger. It's a personal thing...if you want to do so go ahead.
Grips are also a personal things...fit and feel plus aesthetics...again your choice.
I don't normally use any kind of mag well extender. I have one that came with one but again...no big deal to me. Installing one on a competition gun makes some sense but on an Officer's ACP? It kinda gets away from the purpose of a concealable handgun. I'd rather put the effort into practicing quick magazine changes.
We all have different philosophies on what makes a good handgun. For the most part I subscribe to the "less is more" philosophy where what I do with a pistol is only what makes sense for me and nothing more. I do like nice aesthetics though and that can run into as much money as more substantive physical changes to the gun.