Module development and code questions

This is not working for some reason. The form is redisplayed but the textarea field remains empty. Why?

I've installed Drupal 8, I've created a PHP file to read a XML file and insert some items, but I'm getting this error.

Fatal error: Uncaught Error: Class 'Drupal\node\Entity\Node' not found in C:\xampp\htdocs\drupal8\migracion.php:12 Stack trace: #0 {main} thrown in C:\xampp\htdocs\drupal8\migracion.php on line 12

This is the code I am using.

Hi everyone, 

I have a content type "sale" with a field "date", and I would like to delete node automaticaly when date is more thant 7days after now.

Rules en Drupal 8, is a nightmare for me ! I tryed to make a custom module but it's not a success...

Do you have a solution for me ?

Thank you so much for your help !

Just like how the views uses little twig based input field, I want to do the same for my mail message body.

I've copied the form code over from the core->view module, but I am not sure how to set a set of fields to be available to use.

I also tried to use the {{ druapl_field('field_name','node' node_id) }} but this doesn't seem to be working.

Is there a way to set which fields will be available as a replacement pattern or make the function above to work?

I am using Drupal 7 and I want to add a new page with a custom section on top. This custom section consists of some information that we are getting through some rest API. 

I want this custom section on top and client can add html content and sections below that section from the Drupal backend.

I tried creating a custom page--custompage.tpl.php and added that section. That page worked fine but unfortunately, it wasn't editable from the Drupal dashboard and we could not add sections before it so it was of no use.