It depends on how you are gonna use it...
4GB with normal windows 7/8 64bit programs are today's minimum
8GB it's the sweet spot, very few programs will actually fill them
16 or 32GB if actually know you are using that program x which will consume LOTS of ram
Building many machines,my advice is to go 8GB for now with a low latency:
-1600 CAS 8(good)
-1866 CAS 9(very slightly better)
since all AMD cpus aren't exactly monsters of ram bandwidth, a good ram will keep the beasties feeded
By experience corsair,crucial,g.skill and patriot always deliver.
Buy a dual bank kit(2x4GB) since 8350 has two memory channels.
Oh by the way,FX-8350 IS a beast of a processor,it's just that many programmers compile badly threaded programs with Intel compiler, and many reviewers think prime95 and itunes are real world heavy programs.Don't be fooled
have a nice day