Gaming should be fine at 60fps and above, at low to medium settings. Not recommended for streaming, as the PC is unable to maintain both a quality game experience AND a quality stream.
Make sure they are connected to the graphics card not the motherboard itself. Beyond that, it would need to be checked by our service team if still not responding.
Essentially any, just make sure you also have an appropriate cable to connect to one of the display outputs. Card installed had 1x DP, 1x HDMI, 1x DVI-D
Practically everything, down to the motherboard. The most common upgrades would be GPU and RAM (and PSU if necessary) about 2-3 years in the future. Then a CPU and storage upgrade about 5+ years in the future.
That is standard for every PC, it is recommended for better audio quality both in and out. You will need something like this: https://www.pbtech.co.nz/product/CABSTT1721995/StarTech-MUYHSFMM-35mm-4-Position-to-2x-3-Position
We are using an updated BIOS to run the CPU, and can confirm it does work currently. Manufacturers have stopped official support for the Gen 3 APU's in favor of newer ones.