No they aren't. Either there are rules for the location and order of road signs or there aren't. One can't have it both ways.
No it isn't. Either there was a larger first sign or there wasn't. If it doesn't matter to have a larger first sign, why is it done?
That's nonsense. The motorist didn't know what the speed restriction was, or even whether there was one. Presence of road works does not imply a specific speed restriction and unless you were there and know the circumstances, it isn't possible to know what the speed was, let alone whether it constituted dangerous driving.
That may be true, but if this is going to be used as a means of measuring whether somebody is driving safely, then those who would seek to use it must set up the measurement and notification correctly. If they don't, then they must expect to be challenged on it.