Hey Erineeya,
Some links that may help you are below:
Progress Reset After Faction Change
Regarding the question B, and if I understand your question well, the rewards that you gained from the War Campaign checkpoints are not lost. I had a similar situation recently on my own characters, where I reached the War Campaign checkpoint with Baine on my main character, and then I was able to obtain the Heritage armor on my Tauren character.
Just to clarify that does not mean that with a different Alliance character you can carry on from where you were left off. A different character has to have their own path in the War Campaign.