When you use the [adduser] command in Ubuntu 18.x it creats a user directory in the /home directory. From that point forward, every time you login as the new user your default home directory will be /home/new_user
Therefore, the [wget] command is to be run from this new users home directory (/home/new_user)
Once the install.py file is transferred into the new users home directory, then the install command is also run from this new user directory as such:
sudo -H python3 install.py --production --user [def_user]
I am relieved to hear that you have a successful install to work from now. Welcome to the v12 experience. 
BKM