Streamlined Membership Management System

We are an organisation with multiple chapters (different locations across Australia and Latin America) each operating autonomously with their own separate websites, mailing lists, members, Mailchimp accounts etc.
Lists are built by chapter teams through running of events and initiatives at a local level where people's contact details are captured and stored.
We also have one centralised payment gateway and registration system for membership across the whole organisation.
What we are seeking is someone who can design and develop the most effective system for registering and managing our members at an organisational and local chapter level so that we minimise duplication of lists, ensure visibility/distinction made between members (paid members of network) and subscribers (unpaid - on network mailing list)
This includes best integration with Paypal, cross-linking across websites, systematic mailing list merges across Mailchimp accounts so that central mailing list and chapter mailing lists are constantly up to date.
Payment is negotiable depending on the system solution proposed.
We need to ensure this system is functioning correctly before we proceed to the next stage of organisational development which will lead to further freelance project requirements. (i.e. for quality freelancer - probability of ongoing work)