take some baking soda mixed with water to the terminal when its disconnected and scrub away, corrosion isn't all that uncommon. It happens, just be sure to clean it off as soon as it develops. Be happy your sidepost hasn't snapped off. It happens.
As for the wiring choice, as long as the amps are off when the car is off, your battery won't be drained. From a technical aspect, the remote wire on the amp is the best because it gives you the factory operation of the amp. Another one is to have it switched like someone else suggested.
