Selfhosted

Some of these you're already doing, but writing a complete* list. *almost garuanteed not to be complete, suggestions welcome

1. Have everything behind the same reverse proxy, so that you have only one endpoint to worry about. Run it through ssllabs or similar to check your config.
2. On your reverse proxy, add one or more layers of authentication if possible. Many possibilities here: If one app supports client certificates, while another has limited capabilities, you could probably tie together something where IPs are whitelisted to the ither services based on that certificate auth.
3. Geoblock all countries you won't be accessing from
4. crowdsec is pretty nice, this detects/blocks threats. kinda like fail2ban but on steroids.
5. if you use one of those 5$/month VPSes, with a VPN tunnel to your backend services, that adds one layer of "if it's compromised, they're not in your house".

lastly consider if these things need to be publically avilable at all. I'm happy with 95% of my services only being available through Tailscale (mesh VPN, paid service with good enough free tier, open source+free alternatives available), and I've got tailscale on all my devices

Why? Not every service is meant to be exposed to the open internet. Immich is the only one of what you listed that makes sense to have out in the open.