The green and White from the x360 pcb goes to the imp. Vcc from imp needs to go to both the Usb parts of the x360 and Cthulhu.
The small holes at the end of the Cthulhu are for piggybacking the x360 pcb. If you read the welcome sheet for the Cthulhu you’d know what they’re for…
If you don’t have experience with soldering or electronics I’m not sure why you’re trying to tackle a dual mod…
Ground (black) on 360 goes to ground on imp
VCC (red) on 360 pcb goes to VCC on imp
D- (white) on 360 goes to D-2 on imp
D+ (green) on 360 goes to D+2 on imp.
Use USB on imp for usb out to system.
When successfully dual modded you will need to hold down Guide for 360.
Either/or is fine. Electrically, it doesn’t matter. Some folks prefer the screw terminals for ease, I prefer to solder on the unlabelled holes for a stronger connection.