There’s no point jumping into content planning and link building if Google has difficult discovering the content on your website. It should be one of the first things you should carry out.
The goal of a technical SEO audit is to identify all possible crawling, rendering and indexing issues. Some issues will be low priority while some will require immediate attention (e.g., improper application of noindex meta tag on critical pages).
Similarly, some solutions will be more complex than others.
For example, a popular WordPress pagebuilder WP Bakery loads content via JavaScript. When JS is disabled, search engines are unable to see the content and the internal links on the page. This creates a situation where Google and other search engine bots are unable to render the content on the page. This is bad and the recommended solution will be to use a different pagebuilder. However, doing so will require significant resources.
I recommend starting off any campaign with a technical SEO audit, especially for eCommerce businesses that have a large number of products (in stock or otherwise).