I have an alt scholar that i am playing but i have questions. What makes the scholar different then the white mage or astro-whatever?

I am also not sure what the fairies are for. Do they just heal someone on random and if they do then is their a possibility of overhealing and therefore wasting MP

how do i lower the possibility of having 500000 adds come after me, i know that its not good to spam heal cause that agros adds to the healer but should i just focus using DOTS so that im not bringing down my MP so much?