Q: Connect mac mini to iMac screen

It should work just fine.  You will have to use a Thunderbolt cable to connect the two

and you need to boot the iMac in Target Display Mode (https://support.apple.com/en-us/HT204592).

No, not the camera. The link that Woodmeister 50 provided includes

Connect devices to your Mac

A Mac that's connected to an iMac in Target Display Mode can't use the iMac's built-in camera, its USB, ThunderBolt, or FireWire ports, or devices connected to those ports. To use external devices with your Mac, connect these devices directly to the Mac you want to use them with.

As lllaass has pointed out, the iMac will be nothing more than a screen.

You will need to get a USB Cam/mic combo of which there are many that will work with

Macs.