I've got a sld globally inspired by those posts (and a lot of others):
- GeoServer – Creating Stacked Points
- GeoServer Point Stacker: does identify work on non-clustered points?
- Point Stacker in combination with other filter
I'm currently stuck by the GetFeatureInfo behavior on clustered points. Clicking on a single point give me the informations of this point, clicking on a cluster of points only give me the count of stacked points and the empty data structure. See the screenshot of a QGIS usage below.

I saw that there is a ticket about this point but it seems to be resolved.
Let me know if I missed something !