And would you recommend ZFS or not? ZFS needs Server-Ram - is that true? I forgot to answer your RAID-question - i have to admit - i don´t know. As far as i know it is difficult to expand your raid-array after you have set it up... so i am open to any suggestions. I have two 500 GB HDDs here, i want to use for it and add another 2 TB of Storage - i am pretty sure that i do not need more than max 3-4TB of storage in the next 2 or 3 years.
A lot of people would say now - why do you want build your your own server for that... buy a WD "My Cloud" and everything is ok... but my motivation is: i want to learn from scratch, i want to have my data on MY server and not somewhere else, i want it as secure as possible, want it to be accessable everywhere and i want some data redundancy.