Drupal 8.x

I am using Drupal 8.4.1

From the Readme.txt I found here:

http://cgit.drupalcode.org/video/plain/README.md

I found this:

How to Use
----------
* Go to your content type (can be added to any entity type) page (admin/structure/types)
* Go to manage fields and click add field and choose "Video" from Reference
* Click Save and Continue with rest of the steps.

I got to the admin/structure/types page. After that, I'm lost.

Hello everyone,

My problem is the following:
I have a block that is rendered this way:

      public function build() {

             $filterForm = \Drupal::formBuilder()->getForm('Drupal\smeno\Form\FilterForm');

             $renderArray['filterform'] = $filterForm;
             $renderArray['PsRefund_data'] = $this->getPsRefund();

             return [
                 '#theme' => 'Remboursement-Proffessione-Sante',
                 '#PsRefund_build_data' => $renderArray,
             ];
      }

I would like to "Clear all caches" automatically.

Now, I clear cache like this.
Administration > Configuration > Development > Performance 
Push "Clear all caches" manually.

But I would like to execute this operation automatically everyday. How can I do this?
If someone knows the solution, could you tell me it?

Prior to Drupal 8.4 update was easy:

I have a problem when I delete huge data via Rest API.

Problem:
DB size has increased when I had deleted over 300,000 contents via Rest API. DB size has increased from 1.8GB to 7GB.

I checked what file has increased. These file size has been increased.
/var/lib/mysql/cache_data.ibd　440MB
/var/lib/mysql/cache_entity.ibd　339MB
/var/lib/mysql/cache_dynamic_page_cache.ibd　54MB
/var/lib/mysql/cache_render.ibd　50MB

I am supposed to be building a site for a small municipal government. I was wondering if anyone could recommend a good theme to start off with. I did not see anything specifically designed for small municipal governments.

Thanks