While this is an old post, I figured it all out in a couple of weeks and got all my custom bindings done more efficiently. Only the shoulder buttons can be made into modifiers, the attack buttons / triggers are hard-coded in and cannot be made into modifiers, figured what I need to do.

Using Setup B to get rid of X as Jump, that can't be changed in Keybindings for some reason.

Directional Keys:
Up = Quest Switch
Hold Up = Interact with other Players and Resurrect, the Start button on PS4 controller is too small and hard to hold down to resurrect players, it kept giving me issues; this proved to be a better and more comfortable button.
Left = Quick Pot
Hold Left = Quick Slot Menu
Down = Ultimate, easily out of the way so I don't accidentally fire and simple cast.
Hold Down = Command Pets to attack
Right = Weapon Swap
Hold Right = Sheathe weapon

Sprint on Gamepad doesn't need to hold down like the Shift Key, at least the right Shift key has that issue, so its a one press toggle until you perform an action. It also became my primary modifier key as it doesn't drain stamina until you move and has no adverse effects pressing it while standing still.
Left Shoulder = Sprint
Right Shoulder = Jump
Left Shoulder + Right Shoulder = Dodge roll, if no stamina I end up jumping instead. Easier to direction control too.
Left Shoulder + Square = Crouch (if Snipe is bound to that attack key and you're looking at something, it will cast simultaneously and you'll be fully hidden when it fires. Double benefit!)
Left Shoulder + X = Use Synergy
Left Stick button = Ability 4
Right Stick button = Ability 5
Share Button = Mount (Because PC doesn't do a thing)

I didn't realize the middle touchpad on the PS4 controller has multiple functions depending where you press on it. Anywhere in the middle is primary attack, the side edges are auto-run (did not know, LOVE IT), and I really like the mouse-look feature.