The fanbox extras are not part of the "core" story. Some of them are, but most of them are just added context. There's not really a better way for me to upload them. If you want the core story only, just skip them and re-read after.
Depends on your level and goals. Are you purely looking to read? Or speak too?
I took Japanese classes in college, which I found unhelpful (having a teacher to correct your work was helpful though). The explanations weren't great and the practice didn't fit how I learned.
I have studied...