When I think ‘Google-friendly’ these days – I think a website Google will rank top, if popular and accessible enough, and won’t drop like a f*&^ing stone for no apparent reason one day, even though I followed the Google SEO starter guide to the letter….. just because Google has found something it doesn’t like – or has classified my site as undesirable one day.
Taboola (like many websites) would benefit from iterative SEO, meaning its team should make distinct revisions to the SEO page titles, content headers, and other text to see whether rankings improve without hurting their top positions. But they shouldn’t make too many changes at one time or they won’t know what worked and could disrupt rankings. They could monitor rankings after testing keyword-placement scenarios. (Most website pages are indexed within days or a couple weeks.)

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