In trying to discover more information about this topic, I went to the main Google page. I then clicked the "More" tab (at top). I then clicked the "Books" tab. I then typed your topics into the search box. Below is what turned up. It's always useful to remember that many experts have written many books on practically any topic in which we are interested today. Increasing numbers of these books can now be found and even read (in whole or in part) via Google Books. It takes much more time and effort (in most cases) to write a book than to set up a web site, which is why Google Books is usually preferable to Google itself as a place to begin searching for information. In addition, many of the books you can find through Google Books have been read and approved by experts; this is especially likely if the books have been published by university presses. I hope that this link helps you.
I remember reading the relevant chapter on Africa in the brilliant Guns, Germs and Steel, which suggested that geography was one of the reasons behind the success of the early Bantu civilisation. As #3 suggests, the fact that E. Africa is situated in the middle gave it a distinct advantage in history, as the tribes that originated from there had room to expand and also increased trade opportunities.
Civilization didn't start until about 12,000 years ago so it makes no sense to connect the rise of civilization to the rise of humanity in general, which happened around 200,000 years ago.
One major contrast is that East African civilization was influenced to a large extent by trade with other areas. East African civilizations were able to trade much more easily with Northern Africa, with the Middle East, and even with places like Indonesia and China. This was not the case with Southern Africa.