You can try it and the generated data should be good for submitting but the user interface is not great yet.
What's currently specified is just a base to create brand new netkans for not-yet-hosted mods. Eventually expanding the UI to allow editing existing metadata would be great, but is likely much more in-depth.
Primarily this is a web form which results in a JSON file that is sent in a PR to KSP-CKAN/NetKAN. Workflow is pretty heavily reliant on where a mod is hosted. Most fields are also optional. Spacedock, github, and all other hosts (curse will be a kref-able source in the near future) are the current workflow determinants.
Yes, you can try a possibly outdated and maybe even broken version at https://brohlsoft.de/apps/metadata-webtool/
Yes
Install web-dependencies with bower, install python dependencies with pip install -r requirements.txt (in a virtual environment), start main.py and open http://localhost:8080/metadata-webtool/