Erm.. there shouldn't be npc shops that sell the spirits.. that would take away from players putting the value on how much they sell for.. Just like with instruments, no one wants to buy an instrument for the same or more then you pay in the store so no one would buy a spirit in the market or from another unless the price was cheaper then the store meaning loss of profit from the seller.
Having 10 different types of spirit might not be a good idea, it would be hard to tell which spirit does what for one.. They would have to be different colors and then even still it would be tough to tell..
However maybe it would be a good idea.. like when a player dies, depending on how much ap they have, a certain spirit is released.
