Thank you @piggz and @poetaster for your answers.
I am delighted!
Beautiful to see SFOS on an affordable and promising device like the GS5.
Beautiful to be able to try other devices than supported ones.
Beautiful to be free from, mainly, you know who and you know who :–)
Out of curiosity, I wanted to see this UbPorts-installer and VollaOS.
So I began with them, even if not mandatory.
Then I flashed SFOS as described above.
First sight: Perfectly booted, phone works, SIM is seen after some reboots.
But there is only 45MB of free system storage.
I didn’t find how to free some more storage.
Are there some files to delete?