here's the rundown on babymetal:
first album is unique, enjoyable mix of j-pop and metal.
second album simply dabbled in various metal-sub genres (from dragonforce to viking metal)
currently they are a mess, one of the three core members vanished and was replaced by two trannies, it's a long story but it's still unfolding (next major update in about a week)
2 albums and a few new songs.
on sakura gakuin:
most the graduates are active and remain a cornerstone of the thread
follow that advice for visiting the reddit fukei guide. nice and ordered, plus a bunch of links etc.
tons of content, music, a play, a few documentaries, specials, and weekly panels
like 10 albums and a smattering of bonus songs
/bmsg/ itself:
there's an excellent spreadsheet in the op with download links for stuff not uploaded to streaming sites (high definition concerts, complete albums etc)
oh god so much meme magic
check a /jp/ archive for fun/history/autism/to build up your bmsg folder.