1. Is ghusl (full ritual ablution) required if a spot that water did not reach remains during purification? 2. Is ghusl required again due to previous blasphemous statements, and was ghusl obligatory upon embracing Islam? 3. Is it considered disbelief to deliberately read a word that is not from the Qur’an to complete a recitation, and what should one do if Satan whispers thoughts of disbelief when making a mistake in the Qur’an or laughing? 4. Is ghusl a condition for entering Islam, and is wudu (partial ablution) and the Shahada (testimony of faith) sufficient for entering Islam or upon uttering disbelief, and is the Shahada of the Iqama (call to commence prayer) sufficient for the Shahada of entering Islam? 5. What actions must be taken to get rid of obsessive whispers?

Praise be to Allah for the blessing of steadfastness. Waswasa (whispering) concerning purification is from the tricks of Satan, and you must cut it off immediately and not indulge in it. Do not listen to the whisperings about the incompleteness of ablution (wudu') or ritual bath (ghusl).

The ghusl of an apostate after repentance is not a condition for its validity. Scholars have differed on the obligation of ghusl for a disbeliever upon embracing Islam. Some have restricted this obligation to the presence of a factor necessitating it, such as janabah (major ritual impurity).

Adding to the Quran is forbidden and invalidates the prayer. You must repent from it and resolve not to return to it. If you find the Quran difficult to recite, then bow down, and your prayer is valid.

The rest of what you mentioned in the question is from the whisperings of Satan, so do not surrender to him. Seek refuge in Allah from him, maintain your ablution, increase your remembrance of Allah, recite the morning and evening adhkar, and read the Quran with contemplation. There is no harm in consulting a Muslim psychiatrist.