Healing on PS4?

[Estellios]

I would just Focus Target by selecting the enemy, hitting Square or its equivalent on your controller, and selecting it from the popup menu. Focus Target is very rarely a necessity.

As far as L3 goes, you may not want to change it depending on what other jobs you have interest in. A large amount of MNK's damage is from auto-attacks so I usually use the L3 Lockon while repositioning for combos so that my auto-attacks continue while doing it.