Thanks for writing back.
I tried to access your website, but it seems to timeout without any response. Have you enabled any proxy or Geo IP restriction on the server?
To troubleshoot the error 503, I'll recommend turning on WordPress debugging and then checking the server's error logs for any errors or warnings.
( ref: https://wordpress.org/support/article/debugging-in-wordpress/ )
In case, there is no error or warning in the logs, you're welcome to share a clone/snapshot of the website, for further troubleshooting.
( ref: https://toolset.com/faq/provide-supporters-copy-site/ )
Note: I've set your next reply as private again.
As for your specific questions:
1). This code is a combination of HTML and Toolset shortcodes and can be used in the Toolset's "Fields and Text" block, or WordPress' standard "Classic" block or "Custom HTML" block.
( When Toolset's shortcodes are involved, I'll recommend using the "Fields and Text" block over others. And make sure that the "HTML" tab is selected and not the "Visual" tab )
Please note that the code in your first reply included the PHP code too because it was being used in the PHP template file. But the code in my last reply doesn't have PHP code and is using simple HTML and shortcodes.
2). I can't see the page at the moment, but, if the select field is for the language filter, you won't need it once correct language results are automatically showing.
3). One big advantage of using Toolset plugins is that you can assign a content template to your post types so that you can make the changes to the whole template right from the admin area, without having to edit the PHP template files.
Here is a useful guide on the topic:
https://toolset.com/lesson-placement/lesson-placements-1621067-1621091/
Please let me know if you have any questions about using the content templates.
4). If you have already created a view to show the list of documents, you don't have to create a new one.