A "best OS" never exists. Choose the OS you're familiar and not the 14.04 because of the bug in Ubuntu described in the Collabora documentation
Okay, then I will try with Ubuntu 16.04.
This is still needed. I have created a small thread with some additional ressources where everything is explained:
https://central.owncloud.org/t/collabora-online-code-libreoffice-online-with-owncloud/1576
By trying to access the topic I receive a 'Sorry, you don't have access to that topic!' error 
Thanks