@huber70
So your main objective is to save some €'s? (And I agree with you!)
Using your Pi to
serve video's, music and photo's can be done with eg. Jellyfin.
However it will not look as nice as the (paid) site you use for your photo's. That might be a dealbreaker.
The best solution for working on documents while not at home is "The cloud".
If on Windows use Onedrive with (free 10Gbyte?) space.
If a fan of Google use Gmail.com with 15Gbyte space.
Also the free 2Gbyte of Dropbox is an option.
If privacy paranoid (and I more or less am
sometimes) don't.
If you also want to upload photo's and documents etc. perhaps make the Pi work as a ftp server (it works, but I was never a real fan of it, maybe because I never could make I work the way I wanted it to).
And then you need to be able to remote login to move the uploaded files to a place where they can be used to serve them.
To make all of this work is a lot of work (specially if one has to wait for a reply on mobileread.com if running into a problem.
So what will you try first? What has priority? Or what will be the most fun to work on?