you run: source ~/weewx-venv/bin/activate (that puts you in the virtual environment)
If you type wee_ and hit tab twice you should see:
weectl wee_database wee_debug wee_device wee_import wee_reports weewxd
The commands are here in bin.
~/weewx-venv/bin
and your data is in:
~/weewx-data
I haven't used the wee_extension under V5 as I just copied all my V4 data configs etc to the relevant directories in V5.