Visually inspecting the capacitor is usually enough to see if it's bad, it has a convex shaped head on it where the electrical terminals are if this is out of shape its defective or if it's leaking oil.
On the fan, try to spin it , if ther ei sany resistance at all it is defective, other than that you would need a multimeter than can check microfarads up to at least 100,
It could very well be the defrost board, if it works when you push in contactor then its probably the board.
How can I verify that? Can I bypass with a jumper?