Blender noob here. When I apply a texture to my model, sometimes it becomes deformed (circles 1 and 2) or pixelated (circle 3), and sometimes it works perfectly (circle 4). I've tried changing the face to a different texture and back to the desired texture, but it doesn't change anything. This issue persists in textured and rendered viewport shading, as well as in the final rendering.
Before applying a texture to your object you have to properly uv-unwrap your object. You can do it by going into "Edit Mode" than hitting "U" on the keyboard and selecting "Unwrap" form the drop down menu.
With a complex model like yours a simple unwrap is not going to solve all of your issues. So you should go get some more informations about uv-unwrapping from the Blender Wiki or other web tutorials.