Intermediate/Advanced Technical SEO Enhancement -- 2

I am a marketer and have recently begun addressing the SEO issues with my company's site. I have cleared around 75% of the issues myself, but I need some extra help to finish the job. The site is already performing well, but now is a good time for us to get it as close to perfect as possible.

The tasks would involve:
Important:
- Rectify 4XX Status Codes (3)
- Rectify Low Text-HTML Ratios (31)
- Identify and Rectify a URL With Temporary Redirect (1)
- Rectify Issue with Unminified JavaScript and CSS Files (1)
- Rectify 'Your database prefix is set to the default 'wp_'.
- Remove The DISALLOW_FILE_EDIT constant is defined and set to false from our wp-config.php
- Configure site for HSTS preload list
- Rectify the X-XSS protection security header's non-recommended value: "1".
- Rectify the HSTS Max-age security header's non-recommended value: "2592000 ".
- Rectify the Referrer-Policy security header's non-recommended value: "origin-when-cross-origin".
- Ensure page width matches viewport width (32)
- Improve page loading time (32)
- Delay loading images that appear below the fold (20)

Less Important:
- Rectify Orphaned Pages in Sitemaps (1)
- Rectify Subdomain Doesn't Support HSTS Issue (1)
- Rectify Issue With Blocked External Resource in robots.txt (1)

I have collated all of the pages affected by issues into a spreadsheet to make it a bit easier to figure out where everything is.

We have also recently been informed of some issues that are well beyond the scope of my understanding. They are highlighted in 1.png and 2.png in the attachments for this project.

Thank you for taking the time to read this project.

Luke.