I’m kind of loving Zabbix, but not sure if it’s the right solution for your needs. I’d say it would definitely work, but does take a bit of setup initially. This article is interesting, and seems to have a lot of what you want. Not sure if you want to do all of this. https://opensource.com/article/23/3/build-raspberry-pi-dashboard-appsmith
If you want to self host check out Wireguard options like Netmaker, Headscale, Netbird, etc. these all allow you the ability to setup a machine as an exit node into a LAN, and allow LAN to LAN communication. If you are just looking for a VPN and don’t have to self host, then Tailscale might be a good starting point. Figure out the setup you like, then move to a self hosted headscale setup later using that as a model.
I run OpenSprinkler Pi on my raspberry Pi 3 and HomeAssistant on my Pi 4. Works incredibly well for both.
I’d like to highly recommend QOwnNotes with. File system sync like Nextcloud. Superb.