Your setup is very realistic and fits well with how openHAB and similar platforms are commonly used. A Raspberry Pi works nicely as a gateway for MySensors, Z-Wave, Zigbee, or Grove-based sensors, and running a VPN on the Pi is a solid way to securely bridge it back to your home server. openHAB can be installed on your home server and communicate with the Pi either through a MySensors gateway, MQTT, or native bindings (for example Z-Wave or Zigbee), allowing you to monitor sensor data and control devices centrally. A good place to start would be setting up a basic MySensors or MQTT gateway on the Pi, confirming data flow over the VPN, and then integrating that into openHAB. Many people run similar distributed setups, and the openHAB and MySensors documentation has step-by-step guides that make it easier to build things incrementally as your system grows.