What health metrics do you like for usage-based pricing?

I've launched a new company that is doing pretty well with usage-based pricing, but we don't really have many contracts.

Does anyone have recommendations for how to track typical SaaS metrics like Gross Churn? Not sure how to wrap my head around some good churn metrics. Most of my background is in classic SaaS.

Also, any other metrics people like or articles on good ones to have in usage-based pricing models?