Re. [a], the booklets of these Shallie albums are wrong and his name is actually 小竹克昌 with the characters in his given name reversed, and the correct name is in fact read Katsumasa Odake:
https://www.facebook.com/katsumasa.odake.7 (
曼荼羅音楽出版 on that profile is MANDALA-MUSIC PUBLISHING)
GUST got the name correct in the Firis vocal album and end credits.