UVs: yes. You got it.
textures: yes again
Shaders: shaders and materials are somewhat synonymous. They may or may not use textures that map to uvs. The shader ultimately determines how the thing looks (what it’s surface qualities are). Some element may be procedural like noise on a bump node, some may be from textures like color or roughness. All shaders interact with light. Shaders and materials typically don’t transfer software to software. You will have to reconstruct them. This is one place baking can be useful.
Baking: baking is just creating a texture map that can be used as a material property. Like roughness or metalness.
PBR is just a standardized format for shaders so that artists agree on what texture maps will be needed for material creation. It’s helpful to have a standard when working in groups and across multiple software applications.
For sketchfab you want to export textures for any properties your material makes use of and then hook those textures into the appropriate place in the sketchfab shader.
Hope that helps
