hannson

Make a virtual machine and try out some distros. Everyone has a different opinion but I like manjaro/arch linux the most. jumped on to the ubuntu hate train  

You could take a look at Plex. It's designed as a media server, but it can work pretty well as a local media player.

Manjaro. I don't care if it's based on harder-to-learn arch. It's awesome. 

That would depend on your mainboard sata controller, your array type and your drives. Some hdd configurations are faster than others. I'm running 5 wd red drives in raidz6 (2 drive redundancy) and my entire gbit connection is directly writing on the disks, so 120 MB/s write. 
I really wouldn't recommend running ZFS without ECC-memory if you like your data. In this case you are not protected from bit flipping and your entire array can fail just like that. Be aware what you are getting yourself into: 
 
5 In-memory data integrity in ZFS
 
With your hardware, maybe a raid is not a bad way to go in order to avoid buying completly new gear. 
Cheers