Is the concept that Divine Decree (al-Qada wal-Qadar) comprises knowledge, writing, will, and creation, and that the servant chooses his actions while Allah wills and creates them, fraught with ambiguity or influenced by Ash'ari doctrine?

What the questioner mentioned concerning his understanding of the issue of Divine Decree (Qada') and Divine Preordainment (Qadar) is correct. The stages of belief in it are four: knowledge, writing, will, and creation. And the will and choice of the servant are by the will of Allah, His knowledge, and His power, as He Almighty says: "And you do not will except that Allah wills."

As for the Ash'aris' doctrine regarding Qadar, it differs from the doctrine of Ahlus-Sunnah. They deny the servant's power and the effect of his choice. This is evident in their theory of 'acquisition' (kasb), through which they sought to combine determinism (Jabbariyyah) and free will (Qadariyyah). They came up with something that neither conforms to transmitted texts nor is accepted by reason, and in its outcome, it is pure determinism that negates any power or influence for the servant. As for their understanding of 'will' (iradah), it means love and pleasure, and they interpreted His Almighty saying: "And He does not approve for His servants disbelief" as meaning He does not approve it for His believing servants. Thus, they deviated from both transmitted texts and rational thought.