What should a person who frequently doubts his prayer and purification do, starting from ablution and the opening Takbir, and reciting Al-Fatiha, bowing, the number of Rak'ahs, and Tashahhud, in addition to doubting the invalidation of ablution by passing wind or sound, and when he cannot stop the urine during preparation for prayer and feels some of it coming out?

The cure for obsessive thoughts and excessive doubts lies in ignoring them and not paying them any attention. If Satan whispers that your ablution has been invalidated, then build upon the original state, which is the persistence of your ablution. If he whispers that you did not say the takbir, or the tasbih, or recite Al-Fatiha, then tell him that you did so. If he whispers that you prayed one rak'ah instead of two, then consider them two rak'ahs and ignore his whispers, because he wants to exhaust you and deter you from worship.

As for the discharge of urine drops, if it is merely an obsessive whisper, then ignore it. But if you are certain of the discharge of urine, do not perform ablution until its discharge ceases completely. Then, purify your body and clothes, perform ablution, and pray as long as you find enough time within the prayer's prescribed period to perform it with a valid purification.