Drupal 8.x

I am working in the node template. In my content type I have a referenced field to media called 'field_event'. I created a new media type called 'document'. Inside document there is a file upload field called 'field_document'.
I need to print the file name, size and extension all separately in table cells. 
Example: Myfile | 80kb | pdf

This renders the file, link and name.
{{ content.field_event }}
gives me: mypdf.pdf 80.00 KB, This is the name of my pdf

I have read quite a bit about exporting and importing Drupal configurations between Dev / Stage / Production environments.  The thing I am not clear on is how to deal with the databases in those three environments.

Say I have a production site where users are constantly adding new content to the database (d1).  I also have a development environment where I have added some modules that change the configuration of the tables in the database (d2).  How do I migrate the new database from development thru stage to production?

I'm wondering if anyone can help me. I new to Drupal and I've got some issues that need fixing. I've only been using Drupal for about 6 weeks, after being a WordPress dev for a few years.

Here's my problem; I need to make some pages on the website I'm managing password protected but it just isn't working. I've tried a lot of modules (including Protected Pages which is supposed to work but doesn't on my x8.6.16 installation). I've also thought about adding a really simple little script (was thinking of PHP) but it seems that code like that isn't recommended in Drupal.

I see that Bartik and Classy use this piece of code on page.html.twig.

      <section class="section">
        <a id="main-content" tabindex="-1"></a>
        {{ page.content }}
      </section>

What is the purpose of {{page.content}} and tabindex? It is mandatory to use it when I develop a custom theme?

Thanks.

Hello, 

I am trying to add a link under configuration > content authoring but it does not display. 

drupal-8.7.4\modules\custom\rsvplist\src\Form\RSVPSettingsForm.php:

I have searched the forum, tried many of the recommendations, but I can't seem to find a solution to fix my issue. When I try to edit the menu to this site . https://www.immediaprint.biz I get this error: