Simplifying Complex Character Models

Hello. This is my first post here and I’m pretty new to Blender, so I’m sorry if I come across as a big dumb bad idiot dumb.
As you can see in the title, I have a really complex model with a ton of faces and separate objects that I want to simplify, but I’m not sure of the way to go about doing that. Another big thing is the intersecting and interior faces. I’m trying to turn about 164,000 tris (this is with unapplied subsurface modifiers) to about 10,000. If you have any tips, tricks, or totally rad life hacks, I’d gladly hear them. The blender file for the character is below if I formatted this right, so gaze upon and mess about with it all you want.
the GIRRRRL completo.blend (1.75 MB)
Thank you.