It's hard to summarize. There will be many small adjustments, and maybe a few big ones, depending on how hardcore you want to be. I reject the "open source or nothing" approach. Nice ideal. Great way to fail out of the gate.

I'm using Google Play + Play Services for maps, Android Auto, banking apps, etc. I'm also slowly moving to PWAs where practical and testing FOSS alternatives.

The toughest bit so far is family sharing: photos, lists, reminders. Work in progress.

Step by step.