The most common reason is warped rotors. Excessive heat causes rotors to be warp. A brake inspection should be able to confirm cause of excessive heat.

A standard vehicle runs about $275 per axle.

Not neccisarley. Even though brake pads do come with a brake level indicator you could also just have debris or have the wrong kind of pad installed.

Brake pads produce dust but some like ceramic produce less. Semi mettalic produce more and dust is darker in color. If you really see a lot of brake dust, it may be the sign of an issue with a caliper. Have your vehicle inspected.

This depends on the driving habits and what kind of brake pads the vehicle uses. This makes it hard to give an exact time but usually they will last years.

Yes if there is enough metal left on the rotor to not take it below minimum thickness. This will give your new brake pads a smooth surface to seat to.