Total outputted size of the cover is crop area + bleed area. Safe space is just marked in the book but not included in the total size.
White space is just extra space that is shown as red in the book when designing it. It is taken from the crop area so not included in the calculation for how big the rendered cover is.

The spine options are really just fixed or page ranges so different sized books have different sized spines
There is no inside bleed for the cover because it is pulled from the spine. That number is used in the final calculation

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