Here's what all the stats do:


Strength
Attack Power
Damage dealt by puglist, gladiator, marauder, and lancer arms

Vitality
Damage taken
Enhancement Magic Potency
Maximum HP
Damage dealt by marauder arms

Dexterity
Accuracy
Block Rate
Parry
Damage dealt by archer arms

Intelligence
Attack Magic Potency
Damage dealt by pugilist arms

Mind
Healing Magic Potency
Magic Accuracy
Damage dealt by gladiator, thaumaturge, and conjurer arms

Piety
Magic Evasion
Enfeebling Magic Potency
Maximum MP
Damage dealt by archer, lancer, thaumaturge, and conjurer arms
Stoneskin is enhancing magic, so I guess it's effected by your enhancing magic stat. But I don't know if it really does or not.

Yes heals can crit, but it not displayed as a "critical heal" in the chat log, you'll just sometimes heal for more than usual, and it's effected by magical crit potency and magical crit rate.

For hp/mp I think cura is probably better, although you get more enmity with cura.

On 6.) I think you're talking about sacred prism ? If so yes I would do sacred prism+cura instead of curaga, as curaga gives you a lot of enmity and costs much more MP. You basically get the same effect from doing sacred prism+cura. Curaga heals about the same as cura but it's AoE.