Before you do anything you need to have a concrete idea of what's going on.

The chainline for a fixed gear is fixed and is what you work to. It's going to be 42mm with the Formula hub. This is regardless of the 120/130mm spacing. 120/130 refers to the over-locknut dimension and is not a measurement of the actual hub, as such it can be changed with spacers. This measurement tells you what spacing between the rear dropouts the hub is designed for.

Now, the Bianchi Piaggio appears to have a rear spacing of 126mm. This is the over-locknut dimension you want your formula hub to measure to. This is done using spacers on each side of the hub. You generally want buy wheelsets or hubsets already assembled with the O.L.D. you want. For example; if you order from Velomine, you generally specificy during checkout and they pull the right spacing for you.

See here for a better O.L.D. and spacing explanation. http://sheldonbrown.com/frame-spacing.html

As for chain-length, when you buy a chain it comes with excess links. You feed it around your drive-train and then remove the excess links. Taking up the final tension by sliding the rear wheel back in the dropouts.