3. They did a good job, in my opinion. The reason for this is that at the time, very few civilizations (if any at all) had a large road network that kept the civilization well connected and allowed for "fast" information transport. This was not the case in the Assyrian empire, where local governors were required to maintain roads and road stations at strategic points, allowing for faster communication as a result of improved infrastructure.
4. The Assyrian and Babylonian empires were two kingdoms that coexisted. Their cultures were exactly the same. Everything is the same: language, laws, religion... This culture was either descended from Sumerian and Akkadian societies or entirely created by the Assyrian-Babylonians.