Now as you can imagine there’s a gazillion potential solutions how to tackle that, the main problem is to select that one to match your abilities best.
These I don’t know but I’ll try, so in a nutshell:
Install a Raspi with one or better two additional USB sticks and a USB card writer and put it and the router on a small UPS.
Use openHABian for a quick and just-very-little-knowhow-to-use-UNIX-required setup.
Take care to make it a fully remote-capable server install, setup backup and take precaution of disaster recovery ! With 3k miles away, you will be having a very hard time to recover your server when in need.
Keep spare HW ready on location. Pis are infamous for corruption of their SD card, this you need to protect against. Check out this post to change your server setup to NOT write data to SD but to the external USB stick so in case that fails your server won’t. And don’t use “move root to USB” in openHABian.
openHABian has a backup tool called Amanda. The USB stick is also meant to provide storage for backups. Use Amanda to generate a clone of your SD card once you’re done installing, and repeat after significant changes. That’s what the card writer is for so you can clone your server from remote. Should your Pi fail, you can have your remote helping hands person replace the SD card with the clone one (or even the Pi with the spare one if that’s broken). That’s best practice for homes to run your automation on Pis, but even more so if that home is as far away as is yours.
To access your openHAB instance to run there, see here.
You could start using myopenHAB, but that will only give you GUI-level access to openHAB which is ok for monitoring, but it will be insufficient when you need to start diagnosing problems with your house.
I’d setup your router to use a DynDNS like service so it’ll dynamically map a fixed DNS name to its (ever-changing) IP address. You need to make your router forward a couple of ports to your Pi as then you will be able to access the openHAB GUI via browser and the Pi on UNIX shell level using SSH on these ports.
Install NGINX to protect access via GUI (use openHABian there’s an option to auto-setup NGINX).
You should make use of monitoring capabilities built into the bindings you will use for your devices, plus use the generic network binding to ping devices on IP level.
Mid-term you should implement rules using the openHAB rules engine to constantly monitor your devices on application level, auto-diagnose output to the extent possible, and to send alarms if something’s weird or broken. I’m using the telegram binding for that purpose, but there’s many more options.