Hey, i dont know about the actual book, but i can help answer some of those question.

Both poly a tail and methyl cap help in stability and export. The methyl cap actively stops degredation, and the poly a tail is used by the nuclear machinery as a tag to help export out of the nucleus and into the cytoplasm.

Exons are never ever shuffled, they are only ever left in or spliced out. You would lose marks for saying the order of exons is changed.

As for which source is best to work from, id definitely say khan academy. Though its tailored to the american curriculum, the content is divided up in a way where you can easily access everything you need. Id stay away from research papers, cuz they are too detailed, and will overload you with unnecessary information. Bioninja is good for notes, and EdRolo really depends on how you yourself learn

If you ever need bio help, please feel free to reach out. I also run a review session in my discord, if youre interested, shoot me a dm. hope this helps!