Some light reading
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That said it is ETTL. A great tool but is subject to many variables. There is a pre flash that determines correct flash exposure. Much like your camera's light meter (NOTE: The cameras light meter has nothing to do with the flash).
I'm not sure what your intended meaning was but for the sake of clarity, E-TTL II does use the camera's metering system. The 580EX II has an external meter which can be optionally used instead of E-TTL II but it has few if any practical advantages other than allowing automatic flash exposure off-camera when using dumb (non-E-TTL II) triggers.
I keep it simple. Spend enough time to choose the best parameters, and then save as JPEG. I use default sharpening unless I print big.
LR gives you much more freedom in the conversion than DPP. I wish it were not catalog oriented. For people like me, who use it as a converter only, "importing" is a unnecessary annoying step.
It is also much faster. Before LR I converted using DPP and then edited in PS. Add all the resizing and sharpening actions. A real nightmare. LR must have cut my PP time at least in half.
I typically choose Standard for output sharpening. In your opinion which is the better media selection when the client does not know what type paper they will print on Matte or Glossy? I usually go Matte as my guess is most don't go full gloss.
I do not use outputs sharpening, so I do not know. When printing small - does not really matter. For large print, I sharpen in PS. And I am my own (only) client.