1. The configuration is synced immediately throughout the whole cluster.
2. There is not a huge ammount of traffic generated during this time, it is simply propigating the current configuration folder which I dont imagine to be over 1mb (would need to double check that). I dont understand the second part completley, but the sync of the config happens over a secure connection (port 12346, defined under Configuration > Central Managment Configuration).
3. It safeguards it with timestamps, and currently you are only able to login to one "GUI" node at a time. So if you login in to nodeA, then you cannot login to nodeB (it will tell you to login to nodeA, although priority may take precedence). To further elaborate on the timestamps, starting in 7.1, the cluster will establish its own shared time (similar if not exactly the same as NTP), this will ensure that any system time differences will be accounted for.
4. There is no "global" log for all these changes, but each appliance has it's own audit, and storage log. The audit log would be the more human readable of the two. The storage log is a more verbose log which tells you what files have been modified among other things.