Forgot to mention, this is the Kasa app:
In answer to your question about options 1-4...
For Hue, again if you have a bridge, I would keep the lights on the bridge and so they can remain paired with Google as they are now, so option 4.
For Kasa, if you go down the local route like me, that would be option 1, removing them from the Kasa cloud and setting up in the HE app above, then making them available to Google using the HE built-in Google app.
Chromecast would be 4, no change to existing setup outside of HE, simply add them to the Chromecast HE built-in app.
Hope this all makes sense...
Simon