Don't let it discourage you... If you like doing it, carry on and if you have the room then save up your scrap until you have a pickup load... On a furnace you will find the steel casing and burners. The gas valve is aluminum and should be taken apart. There is an electric motor that runs the fan, personally I take the motor in as is. If it's an older furnace, there will be a small copper line going to the pilot light. some wire that goes to the motor. If it's a newer furnace, there will be a circuit board.

have fun.