Thank you very much for your encouraging report, Giuseppe!
Even more, your detailed installation guide will be of real help for installing Ossn on a dedicated server.
There's just one thing to note, though:
Since mcrypt is depreceted and has been removed since PHP 7.2
Ossn kept track of that alredy and is using open-ssl en-/decryption instead.
Hence, as Ossn isn't using mcrypt anymore and you can remove those lines from your guide.