This example has most of the scenarios you have called out: https://github.com/livefir/fir/tree/main/examples/fira. Fir aims to limit itself to rendering templates on the server and making it available for all subscribers as a browser CustomEvent which is consumed by alpine.js for more complex interactivity. The expectation is the that the developer handles it via either alpine.js plugins or standard JS code.

[edit] This is still a work-in-progress so I will certainly add better guides and documentation moving forward. Although its good to get feedback that this approach might be interesting for at least some people.