I slapped together similar (but much less impressive) take on this theme very recently. I use VNC for remote access rather than SSH'ing into my home network directly. Do you opt to just forward a port on your router and send it to your pi's SSH port? I wasn't sure how risky that would be or what options exist for that.
Also I noticed you mentioned a water sensor at the end, I did a similar project for that as well after I had some basement water issues. I just got a couple of super cheap humidity sensors and had them take a picture of the scene and email it to me if the sensors thought they were submerged. Great minds think alike! :)
I don't allow SSH into my home network — I only SSH into the Raspberry Pi to work on, or modify, the alarm system when I'm at home.
For remote access to the alarm system itself I use Home Assistant, which communicates the the Raspberry Pi on MQTT.
I'm, looking at cutting the power to the dish washer, and closing the main water valve in case of a water alarm. And there is a short siren burst every 10 seconds. But this is still very much a work in progress :)
Not GP but may be helpful to someone: I wouldn't expose any home-net service to the Internet except Wireguard VPN. It listens on connection-less UDP and only responds to clients with recognized auth key. On the router you just forward UDP port to the machine with WG. There are clients for Windows, Mac, smartphones.
I slapped together similar (but much less impressive) take on this theme very recently. I use VNC for remote access rather than SSH'ing into my home network directly. Do you opt to just forward a port on your router and send it to your pi's SSH port? I wasn't sure how risky that would be or what options exist for that.
Also I noticed you mentioned a water sensor at the end, I did a similar project for that as well after I had some basement water issues. I just got a couple of super cheap humidity sensors and had them take a picture of the scene and email it to me if the sensors thought they were submerged. Great minds think alike! :)
https://jeskin.net/blog/raspberry-cam-home-monitoring/