I was setting up a NS for a small office (friend) also experimenting the ONLYOFFICE , I suggest that you look into it.
This will definitely replace the collabora online, it goes well with nextcloud as well as it works as standalone.
It can be installed on NS without problems it relies on NGIX , it has iredmail (http://www.iredmail.org/)
Horde Groupware
as part of the suite.
The community version works perfectly fine, free of charge for up to 20 simultaneous connection
check it out : https://onlyoffice.org/
this is a prebuilt for centos : https://sourceforge.net/projects/teamlab/files/ONLYOFFICE_DocumentServer/v4.3/binaries/onlyoffice-documentserver.x86_64.rpm/download
Enjoy