How to create a universal letter template in Word?

Question

Macros

Good afternoon!
There is a letter designed as follows: It is
necessary to make a template that would have the ability to:

1. Filling in all yellow fields
   
2. Block #1 inserts (red rectangle) up to 3 times in a row
   
3. Block #2 exclusion (blue box) i.e. remove from the letter template if there are no attachments to the letter
   

With all this, block access to editing the main (black) text
Question: How can all this be implemented? I think that VBA can handle this quite well, but I think how to run the script automatically, i.e. so that the user does not press additional buttons like "check document" to run the script.
Please throw off links to information on this topic, I will be grateful.