Based on the info I've found, when building surveys from existing feature services using relationships, the GlobalID must be used for the relationship. I want to make sure I'm setting up my feature services properly, can you confirm James Tedrick (see attachment)?
Are there any other caveats or best practices to follow?
This is correct. Please see the following for full feature service requirements: Use Survey123 with existing feature services—Survey123 for ArcGIS | ArcGIS .
When you publish the service, enable sync - this is a good test to make sure the feature service is correctly configured.