Those two problems may or may not be related.
What is the UCS server role (master, backup, slave, member) of the server you are installing on?
ucr get server/role
Regarding the connection error, please look at:
Regarding the installation of OX Documents, please post the output of this here:
And try to install from the command line:
univention-app install open-xchange-text
The relevant logfile is then: