On the server side the resource usage depends on the number of people who are going to use the server simultaneously.
Below is the minimum configuration that should be able to handle the basics:
CPU: 2 cores, 2GHz or bigger
2 public IP addresses
The native IoChat client application is supported on Android and iOS devices. The service can also be accessed directly on the server with a WebRTC supported web browser – Google Chrome, Mozilla Firefox, Microsoft Edge, Opera, and others. Check here if your browser supports WebRTC: https://caniuse.com/#search=webrtc.