Poly and texture reduction of high res character assets
 

Total novice in using Maya though have quite a bit of Houdini experience.
I am tasked with taking existing high resolution character assets, textures and rigs and exporting them for use in Unreal for a crowd scene.
Using a plugin called Atoms Maya.
Just the geometry .ma file is over 1GB, the mocap rigging file almost 2GB and the texture maps over 70GB.

What are the steps involved in reducing the complexity of these assets?

Can anyone point me to one or two good beginners tutorials?
Thanks in advance for your patience and any help with the above!