The G25 should work from USB port number 2 without a hitch. I made my own pedal mount for my G25, I had previously used it with my DFGT. The G25 pedals are big and heavy, it uses 6mm screws (upto 6 I think) for mounting of the pedals. I prefer to angle my pedals in the configuration I have, its more ergonomic. My legs, knees, ankles don't get tired or painful after long driving sessions. See my signature below for my setup.
Added: Not sure if you have used a wheel before? Give the G25 a chance, any wheel takes practice to learn and the G25 is no ordinary wheel since you are adding a clutch and shifter into the mix. Also the button layout takes some getting used to since they are not labeled on the G25. As far as mounting the pedals, this will be dependant on how aggressively you use your pedals while driving.