Are purification, ablution, ghusl, and two rak'ahs of prayer after the intention necessary for the validity of the ihram or entering into the rites of Hajj/Umrah? And is the ihram of one who intended to enter into the rites while in a state of major ritual impurity (junub), and donned the ihram, and entered Mecca on the 8th of Dhul-Hijjah, valid?

It is not a prerequisite for entering into the state of Ihram (definition) for Hajj or Umrah (definition) to perform Wudu, Ghusl (definition), or purification, or to pray two Rak'ahs. These matters are recommended. It is disliked for a person in a state of Janabah (definition) (major ritual impurity) or a menstruating woman to enter Ihram if it is possible to delay it until purification, but their Ihram is valid. A person in a state of Janabah must perform Ghusl to perform prayer and Tawaf (definition) because purity is a condition for their validity.