512mb will be more than enough to run a File Server and you will be able to remotely administer it over SSH after the initial installation(Which while you can do remotely isn't advisable for a new user)
I've never setup a music server before but it doesn't seem like anything too hard, you could run both a FS and MS on the box easily. From a quick Google Sockso looks like a nice bit of software which you can use to stream music from the Server to your PC via a web interface, although there may be better options which I don't know about.
I would recommend you take a look at Linux: The Complete Reference, Sixth Edition if you want to learn Linux. While the instillation and setup guides will tell you what to do and give you the needed commands they wont realty teach you anything, this book provides a great reference for everything a new user will need to get started.(You can also find a free .pdf version of the book with a little looking)