Inisghtful question!

The Qur'an itself does not specify which prayer is the "middle prayer" (salat al-wusta) in Qur'an 2:238.

According to Shi'i hadith (via Imam al-Baqir and Imam al-Sadiq), the "middle prayer" is the noon (zuhr) prayer (and possibly specifically the Friday prayer).

This corresponds with the idea that the sun is in the middle of the sky at this time, and so it is a middle prayer.

Sunni scholars mostly say that it is the 'asr prayer, although some say it is the zuhr prayer, and a few say it is the fajr prayer (as you have suggested). These views are also based on hadith/interpretation of hadith and an interpretation of what is meant by 'middle'.

The Qur'an speaks to us all individually, and I don't think there is any problem if this ayah speaks to different people differently since it is reminding us to focus on our prayers. Some people may need more focus on their fajr prayer (possibly because they are sleepy!), while others may need more focus on their noon/afternoon prayers, because they are busy.

Allah knows best!

This is a big question and one that many people may have different answers on.

In my view, we have to have faith that we received what is necessary for us via the Qur'an and hadith, and ethical principles stated in them, and that we are meant to put forward effort to try to deduce the right answers for our time. This is part of our test and struggle as individuals and as a human race.

We still receive spiritual guidance from Imam Mahdi (A) and of course from Allah, even if it is not in the form of texts.  

In Nahj al-Balaghah, it is related that Imam 'Ali said, "A woman's jealousy is disbelief, and a man's jealousy is faith."

This is generally explained by saying that a woman should not be jealous of her husband for lawfully taking another woman (such as a co-wife), because it is allowed. However, a man's jealousy over his woman will impel him to protect her from other men.

(Sadly, many customs and traditions worldwide regarding women boil down to protecting women from overeager men!)

Either this attribution to Imam Ali is accurate; or, possibly, there is a cultural element to this attribution to Imam 'Ali since many cultures have this sense of machismo.

Al-Kafi also contains a hadith which says that a woman's ghirah stems from love (al-Kāfī, vol. 5, p. 506, no. 6). That is, because she loves her husband, she wants him for herself.

Some narrations discuss ghirah relating to Allah; for instance, because of his ghirah, Allah hates the forbidden things. This is somewhat similar to the idea of sexual morality (just as the womenfolk are described as the haram and off limits to other men, the sins are described as haraam and off limits to people) but is also broader. It seems to be the Islamic way that the Old Testament idea of a "jealous God" is revised.