I have an Olympic AR 9mm. It has a PCR lower and a A2 stock, really heavy 16" barrel. There are is no flash suppressor on it, nor threads at the end of the barrel.
Can I put some type of flash suppressor on it? Should I?
I want to put a nice telescoping stock on it. I was thinking about a RR one. It comes with a buffer & spring. Do the buffer and spring that come with it work on a 9mm upper?
Yes you can and yes you should (providing your state law doesn't prohibit it).
Colt makes a 9mm FS, and IIRC Oly does too (ask them).
No you don't want foldig - you want telescoping.
Yes the standard CAR buffer & spring will work fine with an OLY 9mm upper.