I'd suggest you'd be better off buying a multi-port HDMI encoder over a new Mac Mini. This cc4c extension is great, don't get me wrong, but if you can capture the output from a FireStick 4K Max (currently on sale for $27) or a Chromecast with Google TV 4K there's more scalability.
I use this extension, but my daily driver is a 4 port encoder with 4 Firestick 4K Max devices. All rack mounted and PoE powered, this setup delivers multiple streams without breaking a sweat. The horsepower required for this extension can be a challenge for a single stream, much less when you start considering multiple simultaneous.