Is sending blessings upon the Prophet by saying, "O Allah, send Your choicest blessings upon the most honorable of Your creations, by the number of Your knowledge, our Master Muhammad," correct?

There is no objection to sending blessings upon the Prophet, peace and blessings be upon him, ten times, or more, or less, at any time, due to the encouragement to do so frequently. Al-Tabarani narrated that the Prophet, peace and blessings be upon him, said: "Whoever sends blessings upon me ten times in the morning and ten times in the evening will receive my intercession on the Day of Resurrection." It is preferable that the blessings be sent using one of the Prophetic formulations. It is disliked to say: "O Allah, send blessings upon Muhammad as many times as Your knowledge," and similar phrases, because they might imply a limitation of Allah's attributes.