Drupal 8.x

I have installed the H5P Module on Drupal 8 and have created my custom content type, which is now ready to be displayed.

Upon going to create a view for said content type I discovered that there isn't a thumbnail/preview option the field which will be displaying the interactive video/image, so in the view it displays the full size video/image.

Hi,

I have form that is build in a custom module and using the debug mode I can see its using the core templates currently. But I need to use custom templates to theme the form and its fields. How can I make custom theme suggestions and use custom templates for some specific fields or use one custom form template and all the fields.

Drupal version: 8.5.6

Thanks.

By means of a custom module I compile an order form. This module queries all nodes of a specific content type, reads out name, price etc. and provides an order form in a block.
Result: https://mettler-beef.ch/bestellung

Problem: If I change a product (node), the cache (probably) prevents the rebuilding of the form.

Desired solution: Upon saving a product, the cache for the custom form and, if necessary, for the custom block is to be invalidated.
How can I achieve this?

This one is pretty complex thing and to be honest i have no slightest idea how to do this, especially since i'm beginner in drupal development. My task goes like this: