A module declares the route:

What is the layout handle of the storefront path /custom/feature/?

A merchant gives you the module MyCompany_MyModule to install.
How do you identify which REST endpoints are supported by the module?

You have been given the task of importing products from an external source. You decide to create a custom
module to do this. The class handling the import creates a product for each record, sets the data on it and
saves it to the database.
What do you inject into a constructor to represent each product you create?

The constructor function for \Magento\Catalog\Model\Category contains this excerpt:

With the automatic dependency injection that Magento provides, how is the StoreManagerInterface resolved?

You are tasked with ensuring customers who log into the site are authorized. By default, this consists of ensuring the customers email and password match the values in the database. On this project, you need to verify additional data in this process.
Keeping in mind upgradeability, how is this done?