Somebody used the historical/mythological Hawaiian explanation that is the one I know as the source of the terminology.
When it comes to my own opinion of how to use Mana.
Mana is more often associated with magical skills, thus how you use mana in your story depends on how you use magic on it.
If Magic is treated as a science, then the best would be for Mana to be an outer force that Magicians learn to give shape and meaning through training and study. Academic Study means normalization, so multiple characters could now the same spells, and application of them would give them interest.
If Magic is more of a state of mind thing, then Mana could be the inner power each magician posses and limits them. They need to learn how to control it, and if it's an inner thing then is more likely they can apply it in unique ways.
From what you wrote in the opening post, I surmise that your mana takes a crystalline form. If that's the case your "mages" could be Jewellers, who cut and polish Crystals to generate different types of spells or uses for the Mana Crystals apart from currency (That could be the crystals on their raw form)