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Thank you for your interest in the Intel® Edison Breakout Board.
Even though custom board designs are out of the scope of this technical support team, I may be able to give you some insight regarding your question.
The USB_VBUS should be left unconnected, the reason behind this is that connecting to 5V is only required when the Edison is expected to work as client, and you mentioned you are looking to use it in host mode.
The FAULT and PSW pins are used for control purposes along with the power supply circuit for the USB device that will be connected to the Edison module, but if you won’t use a power supply that requires control, then there is no need to use these pins, so my suggestion would be to use a pull up resistor to 1.8 V for the FAULT pin, and for the PSW pin, I recommend a pull down resistor to GND.
These couple of threads may be of your interest if you want to compare your design with other community member’s:
Edison Custom Board USB OTG FT201X Device
USB Host mode internally
You can also check the schematics of the Edison expansion boards to see how he FAULT, PSW and VBUS pins are connected:
Schematics for the Intel® Edison Board for Arduino*
Schematics for the Intel® Edison Breakout Board
Additionally, you have to pay attention to the USB ID pin. If the Edison is working as the Host device, the USB ID should be grounded, otherwise it will work as the client device. The error "Unable to initalize libusb:-99 " that you had previously was because the Edison was not working as the Host device. It was fixed after you connected the USB ID to ground.
If you have any other question or update, don’t hesitate to contact us.
Have a nice day.
Thank you for your answer.