Bevel Lemsic was... diciplined by the emperor for the oversight of the exhaust tube... it was removed from the second Death Star's design.
Not entirly sure but from what I can tell they picked the date of the attack for three reasons... One: they knew where it was being built Two: it was close to completion, at that point it would be insane to try to hit the station again because of the amount of causalties it would cause, Three: The Emperor was there.
the term Phyrric victory comes to mind when looking at the resourses needed to knock the death star out of commission.
And the little thing you quoted talks about it being the energy field from the local planet that wreaks havoc with electronics and equipment... so are we also going to count the endor shield?