I would guess that most people haven't strayed from the 3 pack of guide rods that came with the gun. I measured the length of the springs that came with the gun, bought a few different weight Wolff springs, and cut them down. In terms of functionality, the gun will function fine with 9lb or higher. I'd recommend buying a 9lb 10lb 11lb, and 12lb Wolff spring and testing them out to see which you like the most in terms of feel.
The grip is a PT EVO. It actually went on with no modification, but there was too much tension at the top of the grip. Little bit of fitting to the top of the grip, and the whole area above the trigger. Not too bad, but it was my first time doing it so I really took my time.