Realistically, what is the lowest refresh rate?

[jangaraj]

Grafana is the right tool, but you need to use realtime streaming and not “page refresh”. It needs some googling and source code digging. For example Snap app was/is able to do that.

Some hints:

How to Stream Sensor Data with Grafana and InfluxDB | Grafana Labs

Does it support customized datasource?

There is no streaming plugin or support for Grafana yet. The experimental Snap App plugin streams live data as does the closed source Splunk plugin. So it is fully possible if someone builds a general purpose plugin for streaming data to Grafana. Or you could build your own data source plugin that accepts data via your pub-sub protocol. Websockets and live data streams are a long-term goal on the Grafana roadmap.