I mostly use this build for Argon Farming in the Void, but you can also use it for farming any crate-loot resources.
Mods:
Aura - Loot Detector is good here since that's kind of what you have this build for. You can also use Energy Syphon if you're struggling with energy and don't have Arcane Energize and swap out Rush for Loot Radar.
Exilus - Rush for movement, but you can also run Loot Radar]. Power Drift, Speed Drift, or Primed Surefooted, which will need a forma to fit.
Overextended, Augur Reach, and Stretch For extra range on The Vast Untime and Pull (if you're using it).
Greedy Pull Is helpful to pull far things within your pet's Fetch/Vaccum range but is not necessary if you don't already have the helminth unlocked.
Primed Flow for more energy which goes well with Arcane Energize or Energy Syphon.
Fleeting Expertise and Streamline for that juicy energy efficiency.
Armored Agility is a flex slot since Xaku comes pre-forma'd with 2 Vazarin. I like Armored Agility since it gives some more move speed as well as armour. You can also run things that give you more survivability, like Sure Footed, Gladiator Resolve/Gladiator Aegis/Carnis Carapace if you're running a melee build, Boreal's Hatred is also good for the shield and efficiency, Rolling Guard is also good if you're running Steel Path content, etc...
Arcanes:
Arcane Energize and Molt Augmented are my favs since I only use these on low-level maps to farm.
A few honourable mentions for survivability are Arcane Grace for healing, Arcane Guardia for tanky, and Arcane Blessing for more Health.
My full Farmer build:
Felarx: https://overframe.gg/build/506640/
Epitaph: https://overframe.gg/build/506657/
Nikana Prime: https://overframe.gg/build/506665/
Smeeta Kavat: https://overframe.gg/build/506635/
The base of the build is Epitaph for AoE-ing the crates when you're out of energy, Smeeta for the luck bonus you can get, and for the Fetch.
Felarx and Nikana can be traded for basically any high-damage weapon you have. I know my builds are quite expensive on Formas, but just take a good primary for damage if you need it.