I honestly would focus more on DH for Red Mage, DH>Crit>Det
But all of what was said above makes sense.
Your weapon you will want 2 DH and other pieces were you cannot add DH you may add Crit.
Now i am not however suggesting you add Dh on everything possible but it also does not really hurt.
I have 1800 DH atm with 1629 Crit and have seen crits up to 25K