What is a good cms that is postgres compatible, open source and either php or python based?
Have you tried Drupal.  Drupal supports PostgreSQL and is written in PHP and is open source.
Php or python
Use and connect to our existing postgres databases
open source / or very low license fees
Common features of cms, with admin tools to help manage / moderate community
have a large member base on very basic site where members provide us contact info and info about their professional characteristics.  About to expand to build new community site (to migrate our member base to) where the users will be able to msg each other, post to forums, blog, share private group discussions, and members will be sent inivitations to earn compensation for their expertise. Profile pages, job postings, and video chat would be plus.
Already have a team of admins savvy with web apps to help manage it but our developer resources are limited (3-4 programmers) and looking to save time in development as opposed to building our new site from scratch.