Is everything the Prophet (peace be upon him) commanded considered an obligation, knowing that some Sunnah acts were mentioned in the form of a command? And what is the difference between Sunnah, emphasized Sunnah, Wajib (obligatory), and Fard (prescribed duty), and where do the beard and niqab fall within these rulings?

That which comes in the form of a command, with emphasis and obligation, is a fard (obligatory) or wajib (necessary) act; its doer is rewarded and its ترك is sinful. That which does not come in the form of an obligation is mandub (recommended), also called fadilah (virtuous) or mustahabb (desirable), and one is rewarded for it. The difference between mustahabb and sunnah mu’akkadah (emphasized sunnah), according to some scholars, is that mustahabb is what the Prophet, peace and blessings be upon him, did but did not persist in or make apparent. As for sunnah mu’akkadah, it is what he did and continuously maintained or made apparent. Growing a beard is wajib (obligatory) according to the most preponderant scholarly opinions. As for the niqab (covering the face and hands), some scholars have said it is wajib, while others have classified it as mubah (permissible) or mandub, unless there is a fear of fitnah (temptation) from uncovering them, in which case covering becomes wajib.