My broader question is: how should I go about to develop verification of consumer published contracts using junit5 and springboot 2? is this a good starting point: https://docs.pact.io/implementation_guides/jvm/provider/junit5spring?

The docs are always a great starting point. You may also enjoy our in browser tutorial https://docs.pactflow.io/docs/tutorials#tutorial and you can clone the repos separately offline to play with after