Again, I am going to recommend Critique of the Gotha Programme.
Marx specifically states that humans are not equal, else they would not be different, and thus have unequal needs and abilities. It is because of this that the goal is "from each according to his abilities, to each according to his needs." This quote specifically comes from Critique of the Gotha Programme.
Hierarchy is unjust if it is in contradiction, if it is through a worker state it ceases to be unjust, and merely becomes what must be done. Engels elaborates on this im On Authority.
Marx was not an Anarchist, he was accepting of administration and a gradual buildup towards Communism.