A: Yes you can as long as the pump is in an enclosed area and not subject to water. Fiberglass should never be exposed to moisture.
A: It will help it from sweating. Cannot determine if will prevent it from freezing up. It is rated as R-3 insulation.
A: This is rated for max temperature of 165 degrees.
A: It would be best to use foam rubber pipe insulation. Do not use fiberglass where it it exposed to rain and snow.