So far these are the only things I have needed for my mac mini:

Elgato Stream Deck. I do a lot of video editing, and this thing is a huge time saver

SD Card reader with long cable. I have my mac mini mounted under my desk, so this sd reader routes up to the right hand side of my desk and is held on with some velcro

Creative Speakers, Pebble v2, also hooked up to the monitor and powered by a usb charging station I have tucked under my desk

I have a monitor with a kvm switch (gigabyte m34wq) that controls my mouse and keyboard via 1 usb-c cable. That leaves one usb-c port open. I sometimes plug in a second monitor via usb-c to hdmi when I video edit. Sometimes I plug in a usb-c portable ssd to transfer files. I have been looking at the Logitech C920S and the Logitech Brio for a webcam, I like the brio for the windows hello since I have a mac and windows, but I don't know anyone that I facetime or video chat with that has a 4k display so I will probably go with the C920s.