I guess I had a couple Q's as well so thanks for watching it :).
One of mine seemed to echo what others asked about the origin/start of the process if II drove I to it. But then, we never saw that progression so we don't know what actually did besides the turning on of the machine.
Clearly the sirens signify that a call was placed to try to put an end to the constant reproductions and should end it. I don't know if they have shelf lives or how they resolve the samsies. It may be best they clip the beginning and the end to allow the story to go the way the author wants us to see it.
I'm not sure if II (III) kept to the script making sure his actions mimicked what he saw himself do to himself because of a fate is fate stance or what. (arm stab, binoc eyes, and red fall)
I kept thinking, do the "murder yourself's self" route (as prescribed by Nick Jays Hamburgers
http://www.youtube.com/watch?v=UeCX3L8glFk time loop scenario) the whole time.
In fact as I drifted off to sleep that night, I mumbled to Noel, "Promise me if you see your clone, you'll murder it first thing, before it can do the same to you." She promised.
Of course there is also the other side of the "to murder yourself or not murder yourself" coin:
http://www.cracked.com/blog/human-clones-do-you-fk-or-fight/