Unless you are already knowledgable with Windows servers, probably Linux is a good solution.
Seriously, if you don't want to learn how to configure and run servers, avoid generic Linux distributions.
What you want in that case is a turnkey thing, like Amahi or FreeNAS (there are others). I've never used a turnkey thing because it's no big deal for me for configure and run a little server. So I can't recommend one specifically.
All the other names you mentionned besides Amahi, FreeNAS and WHS are either for HTPCs or too technical for you to bother with unless you really want to.
And unless you really want to get technical, I specifically recommend avoiding RAID and ZFS. Backups are paramount.
If you want to use free software and are lost, perhaps you should go to a meeting of free software fans close to your place or simply get in touch with the group running such meetings over the Internet. Some of these groups are friendly to newcomers and would help you. And it's sometimes easier if you can meet physically.
That said, it's really not that hard to set up a home server, whatever you choose to go with.