DISCLAIMER: The game isn’t out yet so all of this could be adjusted when we have a better understanding of the mechanics. That being said, this build is a safe bet on damage and allow you to use a lot of guns while going through the story.
Harlowe‘s 
Cosmic Brilliance skill tree has a lot of gun supports so that the playstyle we are focusing on.
Refraction, 
Entangled has the potential to be insane (if double dip isn’t changed drastically). These skills allow our guns to mob and boss well even better if you have damage formulas like with 
Decoherence.
Excited State, 
Critical Funding and Excited State has excellent synergy allowing you to consistently hit crits, entangle enemies and never run out of ammo. And 
Jaunt make for an exciting and fast paced playstyle.
During leveling try to max Decoherence Refraction as fast as possible, then get Critical Funding and Excited State.
