You can try some popular manga reading websites like MangaReader or MangaPark. They often have a wide range of manga available, including Coffee and Vanilla.
On the 'A Journey to the Past' manga wiki, you can expect to see information on the main characters' backstories, reviews and critiques of the manga, and possibly fan art and cosplay inspiration.
I have no idea. You might have better luck asking in manga enthusiast communities or checking specialized manga databases. There could be detailed information there about the specific manga you're looking for.
The 'A Silent Voice' manga wiki offers a lot. It has details about the story development, character evolution, and maybe even fan theories. There's also likely information on the manga's reception and critical analysis.