Regarding not learning on the evening of Dec 24th, my Rebbe told me the reason we don’t learn between Mincha and midnight is because JC in in hell and it is at this time that he begs for mercy and reminds Hashem that he is a yid. The heavenly court then looks down and sees none of the yids learning so JC’s argument gains him no mercy.
May we all be blessed with revealed good and joy!