As the error says you're missing the metric set You need to add
metricsets: ["json"]
And / or
metricsets: ["server"]
Also, if you're just getting started, I would not change anything like the rollover alias. You're just going to cause yourself trouble untill you understand how all that works. I would use as many as the defaults as possible.
Also, I still think the confluent Prometheus endpoint is probably a better way to go.