Thank you for the advice,
I really did not have to change / enable php root directory specifically. The global settings were just fine. I only thought, since joomla heavily relies on php, I'd have to make some adjustments there.
Runs great now.
php is using /tmp for the session save path but there is a work around for that, too.
SMEsitemanager is really one great tool.
Best regards
Stefan Reitz