First off I'm not a minstrel yet so what I have to say can be taken a with a grain of salt.
But I've researched it quite heavily and from what I can tell best build would be
Int>agi>crt
Int gives nice mana pool for buffs
Agi for surviviblity and extra dmg for dragonewt(maybe? don't quote me xD)
Crt for hit and dragonewt dmg aswell
With low health a bishop can easily heal you fully if you get hit and since song cost 10% hp you won't be missing much health.
This is a support/dmg build (mainly dragonewt dmg)
For soloing
Magic Swords (dia, sword amulet, sinbad) would be the best because extra int dmg
Throwing for higher dmg in party's?
This is the build I'm going for once I use a stelfys
Hope this helps ^_^