A: The official answer key uses a mix of Kanji (with furigana) and Hiragana, exactly as the JLPT N5 does. Avoid answer keys in Romaji only.
A: Officially, no. Unofficially, many learners share scanned copies on Google Drive or Dropbox links via Japanese study Discord servers. Minna No Nihongo N5 Renshuu B Answers Pdf