At load time, Hype will only download the smallest set of files it needs to run, so unless disk space is a concern there's no download penalty to keeping the files around.
Your deductions are pretty much correct, but I'll explain each file in a little more depth:
4619AC-restorable.plist
This is basically a representation of the .hype document for restoring from an export. We did this mostly for support reasons - often users would email us their exported document instead of the .hype document and it'd save us a couple emails. Also users sometimes accidentally would trash their .hype document and this is a nice way for them to get back to a working version.
The first few digits are randomized so that a casual browser cannot guess and download your source document; if you really don't want people getting at it then you can disable generation of this file in the preferences as @Photics mentioned.
HYPE-584.full.min.js
This is the full Hype javascript runtime. It is responsible for interpreting the animation data, building the DOM, and driving your entire animation. It is the same for every export. What makes it "full" is that it includes support for IE6-9 and Physics. So if you're deploying on IE or using Physics you must keep this around. In the future we may include more here too.
HYPE-584.thin.min.js
Same as above but does not include support for IE6-9 or Physics. In most cases this is what is loaded.
HYPE-584.waypoints.min.js
When an On Enter/Exit Viewport action handler is used, this file will be conditionally included and loaded to support the waypoints for those actions.
PIE.htc
Used for IE6-8 to provide some CSS3 effects.
blank.gif
Used for IE6-8 to properly display PNGs with alpha channels.
cache.manifest
When "Create offline application cache" in the Document inspector is checked, this file is created as a listing of resources which are to be cached for offline usage. Otherwise this file is not created.
filename_hype_generated_script.js
This document contains all your animation/layout data as well as a basic loader for choosing which HYPE.js runtime file to load. This one is absolutely critical! 
Thanks! We spent a lot of engineering effort each release to make sure download size and network connections are as minimal as possible.