We consider the important emerging scenario of a private 5G packet core supporting proximity services enabling coverage extension for end-devices though relays using WiFi-Direct connectivity. We demonstrate and evaluate the implementation of Device-to-Device communications using OTS User Equipment through the development of a customised 5G Packet Core with Local Area Network capability and a mobile/server application to allow the direct communication, discovery and relay selection between the end-device and the relay(s). The system was tested in a laboratory-based test-bed and latency, throughput and jitter measurements were obtained for multiple devices. We conclude that 5G networks are suitable for industrial applications although current 5G solutions are focused in consumer communications, which require changes in the configuration to have similar capacity and delay both for download and upload traffic. Thus, only Non Public Networks (NPN) with proper frame structure and Sub Carrier Space (SCS) can deliver 5G networks better suited for symmetric communications.