Here my results of further install tests.
Install of weewx-venv to /home/test works as follows:
python3 -m venv /home/test/weewx-venv
source /home/test/weewx-venv/bin/activate
python3 -m pip install weewx
The provision of a new station with weectl station create did NOT work, as I found no way to add my custom path.
Depending on the logged on user, weewx-data is either generated in /home/USER or /root.
In a way, this approach does not seem to be consistently.
Did I overlook something to generate the station using a custom path?
Would it make sense to add a 'path option' to weewx utilities?