Quetzcoaltz isn't familiar, but is a likely misspelling of Quetzalcoatl, the Aztec sky and creator God and another reference to the Sun. Although primarily an Aztec deity the Mesoamerican influences are strong, and the Mayans had their own version: Kukulkán. His 'hunger' refers to the ritual animal sacrifices that were made to appease him, and an artefact is probably lying within one of his temples.
Q. What is the significance of the door code?
A. It's the date of the Philadelphia Experiment.
Q. Can you please explain the email on the final computer?
A. Sure thing. We'll look at it piece by piece:
Email: "The others and I have finished reviewing the Animus recordings from Subjects 12-16. While the Piece of Eden remains our priority, we must continue working to locate and understand the remaining artefacts. I am sure you can understand our reasoning behind this. Although satellite is accomplished to a fair portion of the work for us, we will certainly need to deal with those who are either immune to - or protected from - its effects.
Explanation: There are multiple artefacts that Abstergo want to possess in order to control the world, and they all have different powers. Once the satellite is in orbit most of Earth's population will be under their control, but some people will be immune to its effects. They need to secure other artefacts to help deal with these people, otherwise their plans will be exposed and Abstergo will be under attack from rebels.
Email: "Piece of Eden (no. 3) - We applaud your continued efforts to locate an alternate artefact with the loss of no. 2 in the DIA Satellite Accident. We understand Subject Seventeen is having trouble interfacing with the Animus, leading to delays. As a result, we estimate another 24 hours before your next critical update. In the meantime, we'll prepare an extraction team and set them to standby. We're relying on you to obtain the additional information we require. He knows where the other objects are - even if he doesn't realize it. You MUST unlock that final memory or all of this will have been for nothing."
Explanation: The company is frantically trying to locate another Piece of Eden. They were about to launch a satellite with the second piece but an accident occurred and 20 people were killed. Desmond is being used to find another Piece of Eden with which Abstergo can launch another satellite and control the world.
Email: "Philadelphia Project - Data provided from Animus Subject Twelve indicates that the ship briefly manifested in a future state for approximately 18 minutes. It is unclear whether the timeline is consistent with or parallel to our own. Although we have recovered enough data to reconstruct and repair the original artefact used in the experiment, Administration has refused to move forward on the project, citing paradox concerns. Corporate policy remains in place: any objects found to interfere with or manipulate time must be contained. Artefact will be moved to secure storage."
Explanation: According to an email in Lucy's inbox the door code is 10281943 - the date of the alleged Philadelphia Experiment. It is rumoured that on 10 October 1943 the US destroyer escort USS Eldridge was subject to a top-secret experiment and became temporarily invisible. It has been suggested that it also underwent both teleportation and time travel, and that its crew never recovered. Many went mad, and some were even fused to the ship's bulkhead. This email confirms that the experiment took place and that the Templars were behind it.