If more (enough) vitreous degeneration occurs before pvd, does the vitreous come off easier than usual with lesser risk of retinal tear?

Not really. The amount of vitreous liquification does not correlate with the risk of retinal tears. The vitreous liquified in or near the center and the collapses on itself and peels off the retinal surface. The tears occur if there is a spot where it is more stuck to the retina. Think perking tape off of paper, the paper may tear where outbid "too" stuck fown during the peeling. Hope this helps.
Not known. This is not known. However it seems that characteristics of the retina have more to do with the occurrence of a retinal tear than the characteristics of the vitreous. That is, a thin myopic retina is more likely to tear than a thicker one.