I should also point out that you can perform a test database migration without impacting your production 0.8 instance. Make sure that every time you test the migration, you are migrating from an 0.8 database (this could be your live database or a snapshot) to a new, empty database. Also make sure you do not execute the final migration step since this configures webhooks in bitbucket and cannot be reversed.
If you perform a test migration it is also safe to activate a few repositories in the test 1.x instance and test their pipelines. Once your testing is complete you would de-activate the repositories in 1.x to remove any leftover webhooks from Bitbucket that point to the test 1.x instance.
Let me know if that helps, or if you need any clarification.