There are lots of questions in this thread, I am trying to answer them one by one:
1) justify the text of some elements (I can arrange to left, right, center but not justify)
You can try Toolset Grid block, see our document:
https://toolset.com/block-item/grid/
2) add text before the output of a single field. For example: Trainer: [Toolset custom field output]
You can add a Toolset Grid block, two columns, one display text, one display the single field block.
Or you can add a shortcode block, and display the text + field shortcodes:
https://toolset.com/documentation/user-guides/views-shortcodes/
https://toolset.com/documentation/customizing-sites-using-php/functions/
3) give padding left and right, top and bottom to set the width of the whole page
Toolset Content Template works in the content area, for the whole page, you will need to find and edit your theme file for the whole page, customize it to what you want.
4) an added Divi block in gutenberg repeats all global Divi headers in the editor is this normal as the site contains on every page the same Divi global header with page name loading via the database?
Is this problem related with Toolset plugins?
Please try as I mentioned in my first answer:
https://toolset.com/forums/topic/layout-problems/#post-1891255
Check the compatibility issue in your website
5) when i add a Divi footer via Gutenberg Divi Block, the content is loaded but background and other mark up is not loaded (divi footer is also a global divi module).
Same as question 4), please check the compatibility issue in your website
6) Also can i change the border color an background color of element based on user selection in de backend when inputting a new asset via the custom fields I made? I made radio buttons with hex codes to achieve this. Is this also possible with a background image?
No, there isn't such kind of built-in feature within Toolset plugins, you might consider custom codes, change the CSS styles when user change the options value of the radio buttons:
hidden link