Praise be to Allah, the Lord of the World; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
The Mufassirs (who explain the Qur'an) have various opinions concerning the matter of how the Angels knew that human beings will make mischief in the earth. Some of these opinions are as follows:
1. The Angels assumed that to be so through the special knowledge granted to them by Allah i.e. Allah made them aware of this fact. This opinion is held by Ibn Abbas, Ibn Masood, al-Hasan al-Basari and others.
2. They compared the human beings with Jinns who had inhabited the Earth before and made much mischief there.
3. Another opinion is that they guessed based upon the name of "Kalifah" (vicegerant) because a Kalifah usually settle the disputes among the people.
The last opinion is very weak while the first one is very strong.
Allah knows best.
As for the verse: "… clear signs and supported him with Rûh-ul-Qudus [Jibrael (Gabriel)] …"[2:87].
It does not have any evidence for the Kufr and deviation of Christians.
1. We supported him means We strengthened him, We helped him. This is similar to the saying of Allah about Muhammad (Sallallahu Alaihi wa Sallam). Allah Says addressing the Prophet Muhammad (interpretation of meaning): {… He it is Who has supported you with His Help and with the believers.}[8:62].
2. The Muslim scholars differed in the meaning of "Ruh-Ul-Qudus" in the above verse. Some of them believe that it refers to the Injeel (the book Allah sent with Prophet Jesus (Alaihi al-Salam), while others believe that it refers to angel Jibrael (Gabriel).
The reason Jibrael is named Ruh-Ul-Qudus is that "al-Ruh" in Arabic means 'soul'; the main job of Jibrael is to bring revelation to the prophets which consist of life for all human souls, and 'Qudus' means purity. Therefore, the meaning is that Allah supported Jesus with Jibrael who is pure from sins and evil.
And those who meant by "Ruh Ul-Qudus" the Injeel the meaning is apparent; that is, that this holy book was a source of life for souls since it contained the matter of faith and good knowledge.
So, the verse obviously proves that Jesus is merely a slave from the slaves of Allah because he needs help due to weakness and this is not an Attribute of Allah.
As for your second question we do not know the source of translation that you are referring to in your question. Any way the translation of the mentioned verse in the translation accomplished by Dr. Muhammad Taqiuddin al-Hilali and Dr. Muhammad Muhsin Khan and which is approved by the scholars of Saudia is as follows:
(And fear a Day (of Judgement) when a person shall not avail another, nor will intercession be accepted from him nor will compensation be taken from him nor will they be helped. )[2:48]
(And fear the Day (of Judgement) when no person shall avail another, nor shall compensation be accepted from him, nor shall intercession be of use to him, nor shall they be helped. )[2:123]. The pronoun is masculine, not feminine.
"Aleem" means painful, aching and "Azeam" means great, huge, etc.
Allah knows best.