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?

What is the difference between online and offline shipping methods?

You have created a new section in system configuration under the Catalog tab:

How do you restrict an access to the section using Magento ACL?

You are implementing a custom module MyModule, which provides an implementation of
\Psr\Log\LoggerInterface called \MyCompany\MyModule\Logger.
The LoggerInterface has the default preference declared in app/etc/di.xml.
Keeping upgradability in mind, how do you make \MyCompany\MyModule\Logger the default implementation of the LoggerInterface globally?

A third-party module uses a layout update that changes the template path for a core block from product/view/addto/compare.phtml of the Magento_Catalog module to custom/view/addto/compare.phtml of your custom module. The merchant has a customized version of this template in their custom theme.
What is a consequence of this setup?