Change text and layout of WordPress editor

I have two questions regarding the WordPress editor. Please see picture on the link below for easier understanding of my questions.
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I want to control how, and also make it easier, for different users to post blog posts on my blog. For example, I want to change the term “Tags” to “Cities” and I want to put in some example text in the blog editor.

I understand that these changes will be overwritten in a WordPress update.

Question 1. Where can I edit the template for the editor? For example, I want to put in three Headers in a h3 format and some example text below each header, so that the user understands what the post should look like. He will then be able to keep the headers and put in some appropriate text.

Question 2. Where (what file and line) can I change the Tag and the Category name, in the editor?

Appreciate all help. This is almost the last step before the launch of my new site =).