You are adding a new menu item to the admin backend which will link to a custom backend page.
The declaration of the route:

What do you specify as the menu item action attribute value so it links to /admin/mycompany/mymodule/?

How do you pass an array ['one', 'two] as a parameter to you block using the layout XML arguments directive?

You have configured an event observer to watch the checkout_submit_all_after event using this XML:

What is the required class definition for the event observer?

You added a plugin declaration to MyCompany/MyModule/etc/di.xml:

What will be the effect of this declaration?

You have created a module to show manufacturer-list, but in your page need to show Pagination that already ready in your block. Keeping maintainability in mind, where you call echo $block->getPagerHtml();?