It's interesting what you found about this packet. Actually the way the data is stored in this packet is not the "final storage way" because then when the server ACK this packet, it sends again the data and it's not formatted in the same way. So it could explain the low ID range for starting characters (you have access to only a few items on the character creation screen).

I started to reversed that one or two weeks ago and had no time on reversing since so I cannot say much more on that. Will get back to it asap. If you look at the doc on the github wiki you will see what I found on this packet.