I am currently in the process of research/accomplishing this goal. Here's what I have found thus far and what steps I'll be taking next.
1) You can use the GoPro USB device, but there will be significant lag due to high latency. Because of this, it is recommended that you get an HDMI capture card. To answer the question, you will need a Micro HDMI to HDMI cable connecting the GoPro to the capture card. You will also need a USB 3 to mini/micro/etc. cable to connect the capture card to your computer.
2) As stated above, it can be accomplished as a USB device, by using to gopro-py-ap. However, the high latency suggests that this option is non-ideal.
3) There are numerous different video streaming apps, but the main recommendation is going to be OBS, as it is designed for professional recording, and thus has been worked on extensively. That being said, things like Cheese, can be used to tap into the feed. Any meeting apps such as Jitsi or Zoom can also access these feeds.
Here are the resources that have helped me thus far:
This answer will be updated if any more details emerge.
Hope that helps!