Character Configuration > Hotbar Settings > Expanded Hold Controls

You can have up to 32 actions/macros set up doing this, you currently only have 28 class/job/cross skills you can use as a PLD in PvE if you add in LB. That leaves you 4 more for tagging/targeting mobs.

I'm also on PC with gamepad, and have my F1-F12 keys bound to actions. I have more than enough buttons for any job.