I have had positive experiences with both Radicale and Baikal. I am not sure about the Home Assistant integration, but they both use CalDAV, so I would be surprised if there wasn’t a way of connecting them. iOS has native support for CalDAV, but Android needs the davx5 app (free on F-Droid).

I just run some simple services, such as Audiobookshelf or Wallabag, behind a reverse proxy. After reading the other comments, it does not look like there would be any benefit for my use case.

Yes, I have always used a reverse proxy which seems to eliminate the need for multiple IP addresses. It seems like having multiple IP addresses just creates additional cost and complexity, but I have seen many VPS providers offer multiple IP addresses, so I was curious if there was a use case that I was not aware of.