The hardest thing people need to ween themselves off of is email, which I didn't see mentioned here at all.
Many people don't think there are viable Gmail alternatives, but on Drew DeVault's recommendation I recently switched myself over to using Migadu[1] and the experience has been fantastic.
That said, I am running CalDAV and CardDAV at home on my own hardware, but they do offer a simple version of both that should be usable.