if you only use one powermill session at a time, then the API would be a better tool to use. You can find the documentation on the Powermill/Powershape API forum, this post in particular. If you have an existing Visual Studio project, it is easy to add the necessary code to connect to powermill. The documentation in the linked post is easy enough to read that even a feeble-minded person like myself was able to make sense and use of it.
Feel free to post on that forum with API questions. As for plugins, they've made it clear that those questions belong on this forum.
There's plugin documentation located here: C:\Program Files\Autodesk\PowerMill 21.0.30\file\plugins\documentation
Plugins are a bit more work up front, but worth the effort. If you choose to go this route, pm me and I can help you a bit more.
the numbers never lie