Thanks for working on this! On the whole the proposal looks good and well thought out.
About adding a new member:
Members are added to the Packaging community by a simple majority vote by the current membership. Quorum for adding new members is 50%.
A vote to add a new member is triggered when a Packaging community member calls for one publicly on an appropriate communication channel, and another Packaging community member seconds the call within two weeks.
The vote lasts for two weeks. Packaging community members vote for or against.
Two weeks feels a long time, compared to the one week vote for Python core membership (PEP 13):
It is granted by receiving at least two-thirds positive votes in a core team vote that is open for one week and is not vetoed by the steering council.
One week feels about right for core team votes (and still feels a long time when the vote is about your own potential membership!), perhaps also use one week for Packaging community votes?