There are other parts of SEO which you should pay attention to after your audit to make sure you stay competitive. After all, the technical foundation isn't the end of the road for SEO success. It's important to pay attention to your competition's SEO activity, keep an eye on the newest search engine best practices, and maintain local SEO best practices if your business depends on customers visiting a physical address. All of these are elements of a successful SEO strategy and should be corollary to your audit and ongoing SEO maintenance.
Brian, I’m going through Step 3, which is referring to the one version of the website. I found a very good free tool (https://varvy.com/tools/redirects/) to recommend. It checks on the redirect and gives you a visual number of hops. More hops mean more delay. For example, if I use your manual method to check on https://uprenew.com, all looks good. However, if I use the tool and check, I realize there is an unnecessary 1 hop/delay, whereby I can fix it. Hope this helps. : )
The audit is for all pages and not only one. What happens in the majority of the cases is that pages / posts have similarities so you can group them together. For example the pages of a website may be ok but the blog post pages may be missing titles. It’s a lot of work especially for a 500 pages website but you can start from the most important pages first and work your way to the rest