Is knowing that "There is no god but Allah, and that Muhammad is the Messenger of Allah" sufficient for one to be a Muslim, even if they are ignorant of the rest of the pillars of Islam, and what is the minimum one must know to be a Muslim?

Whoever pronounces the two testimonies (Shahadatayn) is considered a Muslim and is treated as such if they comprehend their meaning and believe in them. This is evidenced by the Prophet's (peace be upon him) interaction with those who pronounced them, as in the Hadith of Usama ibn Zayd. Thereafter, they must disbelieve in anything other than Allah, act in accordance with the requirements and conditions of the testimony of Tawhid (Oneness of God), learn and believe in the remaining pillars of faith, and adhere to the rights of the two testimonies, which include submission and surrender to the Sacred Law.