Do we need to define our new 2.0 plan structure in the test environment and sync to live, or do we upgrade the live environment first and define plans after?

You need to use the template for giving the inputs for converting PC 1.0 plans and addons to PC 2.0. Using the inputs, a clone of your live site will be set up for first to validate PC 2.0 data, execute code changes at your end and do end-to-end testing.

To know the complete migration process, click here.