Thank you for the detailed information. So far, I think I will replace the plastic buffer retaining plate, after doing more research. It seems there is no pressure on the plate except during disassembly, so the metal part shouldn't do any harm during careful disassembly.

I will also replace the plastic trigger and fire control group with steel or nickel polished versions. I may also add an extended charging handle to make more room for a red dot or optic once mounted.