How sound is the permissibility of swearing by the Prophet, the validity of the phrase "Were it not for Muhammad, Allah would not have created creation," the legitimacy of celebrating the Prophet's birthday and undertaking journeys to visit graves, and the necessity of Sufi orders, and does the Prophet's leaving something not indicate its prohibition?

Swearing by a created being is not permissible. It is not correct to say that if not for Muhammad, Allah would not have created creation. Celebrating the Prophet's birthday (Mawlid) is not permissible because his abandonment of it, despite the existence of what some believe necessitates it and the absence of any prohibition, is a Sunnah. Undertaking a journey (شد الرحال) specifically to visit the grave of the Prophet (peace be upon him) or the grave of anyone else is not legislated. It is not correct to say that Sufi orders provide sound Islamic upbringing.