CC - If God wants his "institution" to be organized, why didn't he send the prophet earlier than Moses or Abraham so that both of them will know the book and both of them will be following the same path?
VB - First of all God knows better what is right and what is wrong, what is good and what is bad (AL-HAKIM); he always have reasons for each and every activity or movement happened and going to happen. Regarding Prophets, there were over 124000 messengers were sent in different areas, zones and Time to spread the message of LORD. Moses and Abraham was well aware of this fact and informed their people; but due to the passage of time and corruption in the earlier holy books, the message about the last prophet was removed. Quran was clearly saying that all messenger of Allah brought the same religion called ISLAM and they were all muslims.

CC - Why did he gave us freewill? He could've created us to be like the angels who knew him from the start, and just do whatever he wills?
VB- Freewill is been given to humans and Jinns to Test Their Faith as A muslim and reward to the tolerance, chastity, piety and submission of their desires and will to ALLAH and his prophets commandments.

Why would he send a prophet in the past to decide the salvation of the future? What happens to those who had come before him who haven't read the book? What difference does it make, they also don't know the prophet then?
VB - As explained above, a long series of various messengers been sent to a particular zones, time and people/community (around 124000). While the 'Last Prophet' Muhammed (SAW) was sent for the whole humankind covering the period when he attained the prophethood till the day of judgment.
The responsibility to carry the message of Religion of Islam was given to the Saints and see around the globe how this religion getting spreaded and people are more interested and curious in knowing and understanding this religion. The people of past (before Prophet Muhammad (SAW)), had to follow whatever was commanded to practise by then Prophets and will not be questioned what is been instructed to us such as Alcohol is haram for us; while it was allowed to earlier Ummah hence they wouldn't be questioned but if today any christian or jew will convert to Islam then He should follow as per Quran and Sunnah's instructions. There is a tree of all major Prophets and messengers, will share if needed.

CC - Since the prophet only lived in the Middle East, what happens with those people who lived on the north, south, west and eastern part of the world during or prior to the prophets time?
VB - The commandments of Islam is Universal and spreaded all over the World by now. In Quran, He said each and every person in the universe will receive the message of Truth and Islam at certain point of Time in Life and that is His duty to send somebody carrying Allah message in someway........(What I am doing here is also a source of communication and message of True Religion getting across people called DAWAH) Google it Dawah and see how many websites to Spread Islam are available that shows Indeed Allah (SWT) said truth that nobody will be deprieved from HIS message and religion.

However Allah know the BEST!
Peace