Game Input MultipleXer

Nah, some games like Forza did not provide any telemetry interface, or maybe dev did not want to support it

It should work fine.

It will work but no "hard - easy" feeling just on and off

Please provide log file for investigation.

At the first time I also tried with arduino builder. It was successful in uploading firmware too but later I found that uploading with gimx-loader is much easier

I think he wanna use authenticated ds4 with keyboard and mouse at the same time. Yes this is possible, some configs include profile 3 to use a ds4 along with mouse and keyboard.

Do you mean "on-board UART interface"?
I have no idea about performance between connect through usb port and connect on-board UART interface. Maybe you should ask Matlo for advice.

Hello, On wiki you gonna see this line: "RPi support should be considered as experimental. The USB controller has been unstable since the first version. Be prepared to face issues if you try GIMX on the RPi." :D You can also try official distro - Raspbian Stretch for the most compatibility.

Try to unplug and replug gimx adapter/dualshock 4.
Btw, use imgur.com to upload your screenshot.

I have tested USB soundcard on Xbox and it didn't work. As Xbox one did not support it.