>>380619753
>I just bought a couple of avatars and want a breakdown on optimization as a beginner.
Best thing to do is combine all meshes (in blender) that you'll be using and delete all meshes that you won't be using (in blender). I like to keep the face mesh separate so you'll end up with one face mesh that's got all your expression blendshapes on it and one body mesh with all other blendshapes deleted.

Do be careful that some outfits use blendshapes to remove parts of the base body to avoid clipping issues.

Then combine and atlas the material and textures (once again in blender).

Most booths come with sub 70k polys, so that's really all you need to do in order to hit the "good" rating. Shader autism can come later, since booth authors usually give you shaders that are good to go out of the box.
Check the VRC docs for avatar ranking breakdown and set your design goals around it.
https://docs.vrchat.com/docs/avatar-performance-ranking-system#pc-limits