Is there a word for over-thinking actions that should simply be done?
Overthinking is a pretty good choice already:
think about (something) too much or for too long.
Lexico
However, if you want to be fancy, you could use Shakespeare:
Letting 'I dare not' wait upon 'I would' (like the cat i' the adage)
Is a famous quote by Lady Macbeth when she was trying to get her husband to kill the king.
Macbeth Act I Scene VII.