NAS Help!

Hey guys I am looking to put together a NAS and want to use free NAS as my OS. I have a old dell that needs a new power supply and bigger hard drives to hold my data. Do you guys think an old Athlon 64 X2 with 1g of ram will be ok or should I by a new hardware, or a premade one? All I want this to do is exist as a Plex server.

How many hosts will be accessing your NAS? I don't see why the CPU would cause an issue, but according to the freenas wiki there's a rule of thumb of 1GB RAM per 1TB of storage (