The important bit is really that the 'final 5' and those who were on Earth were human, they simply were altered from their original forms slightly and also developed 'regional' genetic mutations on Earth. The 'skinjobs' were made in human image, but they were modified heavily to produce superior strength, guile, etc. The full circle isn't that the 13th colony was the servitor-race of the other 12 on Kobol, it was that they were in fact humans themselves.
To my understanding, this is inaccurate in that they were absolutely cylon, not human.
So ordering your events:
Humans live on Kobol (12 tribes)
Humans create Cylons
Cylons evolve into or humans create(whichever) humanoid cylon models
A falling out occurs, presumably over mono vs poly religious ideas, and the humanoid cylons leave Kobol and settle on earth (The 13th tribe), begin to procreate sexually
Some kind of (civil war?) holocaust occurs on earth, the "final 5" rediscover resurrection and flee earth in search of the 12 tribes
-At some point the 12 leave Kobol, colonize elsewhere(Caprica, etc.), a few thousand years pass, this whole part is grey
The colonies created after the 12 left Kobol reinvent cylons to use as slave labor
Cylon slaves rebel, theres war etc., eventually armistice
Ellen etc. (remainder of the 13th) find the cylon rebels, give them humanoid bodies (the other models), give them resurrection
Cylons attack colonies, nuke everything, 50k escape on galactica etc.
At any rate, the destruction of earth is definitely not Cavil's doing. 13=cylons created on kobol, move to earth, destroyed themselves, 12=humans, left kobol, reinvented cylons thousands of years later and nearly got exterminated by them.
Looking forward to not changing out of my track pants, getting high, and binging the shit out of this show. Wheee spring break.
