if you want to be a strong water HEALER, you will need lots of INT, because it depends on how good your support skill perform, e.g. more INT = more hp healed with cure spell, more sp healed with maigc recovery, more sp extracted with soul dodge.

You will also need a good amount of CON, just to make sure you stay alive. Get a bit more WIS if you want more sp capacitance, since reviving takes 109 sp each time!!!

But you said you have volley skill, so you want to have more ATK and be a warrior??? Volley skill needs LOTS of ATK to do decent damage, so you pretty much have to be a fire/wind warrior at the beginning to use it effectively...