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?

Quoted: Can I put some type of flash suppressor on it?  Should I?

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).

I want to put a nice folding 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?

No you don't want foldig - you want telescoping.

Yes the standard CAR buffer & spring will work fine with an OLY 9mm upper.

Thanks for all the help.  You are right I didn't mean foldings stock.....I meant telescoping.