Is it permissible to single out the mention of the Prophet by calling him "Muhammad" only? What are the levels of addressing him? And is it permissible to invoke blessings upon the angels?

It is not permissible to call the Messenger, peace and blessings be upon him, by his bare name, due to the Almighty's saying: "Make not the calling of the Messenger among you as your calling one another." The scholars have drawn attention to the fact that Allah the Almighty addressed the prophets by their names in the Qur’an, but He did not address the Messenger, peace and blessings be upon him, by his bare name, but rather by his attributes, such as: "O Messenger" and "O Prophet." However, naming him by his bare name in a narration from him is not problematic. As for praying for the angels, there is no harm in it.