i think stoneskin is a bad way to start a fight. im not sure how the emnity works in ffxiv but if damage taken creates emnity, then stoneskinning at the beginning is just going to hurt ur tank's emnity gain more than help it.

if the tank has healing spells, its better to have him take some damage, heal himself a few times, then everyone can jump in cause he would have built a good amount of emnity from damage taken and damage healed.