It might be helpful to know what your experience is with PHP, frameworks, and composer, as well as perhaps your goals. Not necessarily all of those items but with some of that info we can better steer you in the right direction. The skeletons are often the way to best see how Slim can be put together rather than wiring it all yourself. That’s why they are shown as easier ways to get started. If you’d like to build it up yourself you are always welcome to do so, but that will take more work and background knowledge.
In your initial question, since you are within the context of
$this->renderer refers to the
renderer entry from the container, found here.
composer.json file will list what packages are included/installed with your project. You could certainly remove some of them, but obviously any code that depends on those packages will fail.