Some parts, such as the technical site audit, could be easily outsourced, while other parts cannot. SEO affects almost everything you do on your site so you'd have to outsource pretty much everything from site setup to keyword research to writing to getting media quotes. I think it's really important to have a solid understanding of SEO for any website owner whether you're DIY or are hiring out. There are a lot of people/companies willing to charge for bogus SEO work that won't even help your business (and may even hurt it). If you know the fundamentals of SEO you can at least assess whether the SEO company you're hiring does good work or not!