There seems to be a community of testers that share war stories and develop Best Practices and invent new modules. So how does one find that community? Where is the documentation on the details of these environment variables and other settings, how to tools and CPAN uses testing, etc.?

For more information on this community of testers, see qa.perl.org and wiki.cpantesters.org. A lot of their work is done on the perl-qa mailing list and at annual perl qa hackathons.

Like you, I struggled to find definitive references for the latest innovations and conventions the (very active) perl-qa community was concocting. I wrote a short node, Perl CPAN test metadata, a while back which might be of use, especially "The Oslo Consensus" section and References. See also RFC: How to Release Modules on CPAN in 2011.