Plus one for Kavita. Only slight bump is that it wants books to be in series because it’s quite manga focused.

+1 for Uptime Kuma, I use it with ntfy. If OP doesn’t want a self hosted solution, there’s UptimeRobot - essentially SAAS Uptime Kuma, but with a free tier.

Forgejo + Tailscale. Forgejo is the app behind Codeberg so it’s battle tested. I switched to it from Gitea after the controversy.

Forgejo - actively developed open source. It’s what powers Codeberg. Easy to set up and manage with Docker. I moved to it from Gogs and skipped Gitea after reading about the forks.