To remove the rust, remove strings, cover your soundhole(to keep debris out), and lightly go up and down the finger board w/0000 steel wool until the tarnish is gone.(be careful : don't let the steel wool contact anything except the fretboard)
Replace the strings after applying some fingerboard conditioner.(follow pkg directions)
Before you replace the guitar, use a hair dryer to insure there is no excess moisture inside.
A Humidipak will regulate the humidity in the case and guitar.
Hope this helps.
Steve