I have a Brasilian version, but the process is more or less the same...
As for the sight, make sure you use a one piece mount; it will hold up to the recoil a lot better. I have used both the B-Square and the Beeman, and both worked great. As for the scope itself, I am using a BSA 30mm 2-7X Air Rifle scope, and it's held up great. Great optics (I hunt mostly in dusk conditions, with some night hunting too), and can handle the recoil. Magnification is good, but it could be better. A 40mm scope should give you even better optics, all other things held constant, but make sure you get a mount that can handle the larger diameter.
Felipe