I've just read L2girl's guide for spectral dancer's, and tho this won't be my class I understand it's pretty much the same for all. However, I've been told by several ppl that I need 300 moonstone shards for 3rd change, yet no mention of this in L2Girl's guide. I want to be a soultaker, and have been collecting shards in readiness - but do I need them? I know I need 100 shards for subbing, but I'd rather be a soultaker first ;)
Alas, my clannies Necro sub is not yet ready for lvl76 so I don't have specifics for ya. But I have not heard about moonstone shards for your class quest.
I will say I was surprised when my clanny did his Sword Muse quest. He had to go fishing and get a specific fish to deliver at the Hot Springs. He's doing a walkthrough for other SWS shortly.
Keep collecting those shards UNTIL some nice Necromancer/Soultaker can post a specific answer.