The package you have bought may be using multiple Bone layers. To find the hidden bones, go to the Armature panel found in the properties panel and look for the Skeleton drop-down menu. Try clicking through the Bone layers until you find the desired bone. Screenshot: https://imgur.com/a/DIFQsEi

No worries! Here's a link to the official documentation for rigging on Blender's online manual: https://docs.blender.org/manual/en/latest/animation/armatures/index.html

The Subsurf setting may be set too high for your computer to handle. Find the Subsurf modifiers for the meshes and lower the Levels Viewport setting. See screenshot: https://imgur.com/a/DeLp4iA

You can contact me through the 'Contact Creator' button on my Blender Market store or shoot me an email at krisego3d@gmail.com.

To add the Lego PBR Shader to the model, you'll have to go to File->Append and then navigate to where you have the .blend file with the Lego PBR Shader stored. Once you've found the .blend file, click on it and navigate to the NodeTree folder, and look for a node called LEGO PBR SHADER. This node contains all the nodes for the shader, so once it is appended to your current .blend file, you just have to search for the shaders when making the materials (Shift+A and then search the name of the shader you want).