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.
However, if possible, I would like you to expand a bit on your “zombie pages” tip..we run a site where are definitely enough pages to delete (no sessions, no links, probably not even relevant with the main theme of the site, not even important for the architecture of the site)..Nonetheless, I am not very sure what is the best technical decision for these pages…just deleting them from my CMS, redirecting (if there is a relevant alternative) or something else? Unindex them on Search console? what response code they should have? ..
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