The best way to install Drupal 8 is by using Composer. There are several options, but the most widely used and easiest way is to use Composer template for Drupal projects.
Hierarchical Taxonomy Menu is a Drupal 8 module for creating menus from taxonomy terms.
If you are building any kind of API then you now, or at least you should now, that limiting the number of requests is one of the most important parts of your system. You don't want to allow anyone to hammer your endpoints without any kind of limitations. The more popular your app is becoming, the more you have to care about protecting your API endpoints.