You don't use the counter in the Rule Editor. In the When condition inside the Foreach, you would use Segment.{LinkToSER.Identifier}. Below is an example that is similar to what you have.

For the hurdles section:

1. At the moment, I always load the most recent version of the Production Validator available to download from WRC. This ensures that you always have all the classes listed in the documentation. I think in the future this may not be needed but currently this is a good practice.
2. I think this a little vague but maybe on purpose because you can name that new TESTING_NAMESPACE anything you would like.
3. If you are trying to simulate differences probably the best path would be to do the optional steps of running the ConfigureNamespace and Import methods separately. This would allow you to run ConfigureNamespace to create the namespace then you could manually make changes to code to ensure there will be differences in your output after you run the Import.

For the outstanding questions:

1. BPLs are handled just fine. I have a couple in our environment and haven't run into any issues using the PV. As long as the code exists in the environment, PV doesn't care if you are running standard Rules and DTLs, BPLs, or a custom class.
2. Yes, more of this could be scripted. I believe in the last iteration of the code more of the commands needed user input. Looks like they have made a lot of good progress with this latest version so I can only imagine more will follow.

5. In order to run the complete test again where messages are completely reprocessed, you would need to delete the TESTING_NAMESPACE (whatever you called it in the ConfigureNamespace method), copy the original IRIS.DAT from your source to your folder, then start the process again. That clean up could probably be added to the documentation.