IOT Engineer/Developer for MQTT/IoT Remote Deployment

We need to deploy sensor to 50 residential properties, each property will gave up to 10 sensors/devices:
- Power Meter (Volts, Amps, Power)
- Relays (for switching on/off loads)

This is a temporary trial so needs to be cost effective. After some research we are leaning towards:
- Shelly Monitors, Smart Plugs and Relays in the properties using MQTT
- Local 4G gateway installed to create a WiFi network
- Data sent over a VPN network to a central server running Open Automation Software (OAS) and a MQTT Broker
- Data sored in SQL Database in Azzure

We need to prototype a instance of the above, and need help with:
- MQTT Configuration (broker, client settings)
- VPN Configuration (we use Teletonika gateways with their own OpenVPN service)
- OAS Configuration
- Security

If the porotype can be quickly shown to work, will then need ongoing support to deliver the project.