Next.JS - Need a JavaScript developer to help with SEO tasks

Hello! I have a work in progress project with another developer, but we need help with ensuring the site is set up optimally for SEO. The tasks that need completed relate to the following concepts.

Javascript
XML sitemaps
Site architecture
URL structure
Structured data
Thin content
Duplicate content
Hreflang
Canonical tags
404 pages
301 redirects
tags

Specifically I need help with:

Implementing SEO specific pages
Implementing SEO best practices and advice from an SEO/Marketing expert - Here's the current report. We need to fix all of these issues, implement all suggestions, and then re-run the report. From there we will need to do another round of fixed.

There are 9 core page designs for the site (I will need you to implement another 2), but the site is comprised of >4,000,000 pages so SEO is of paramount importance, so I really need your help with this part of the site.

The stack we are using is:

Github
Vercel
Firebase
Next.JS
(Prismic - for some assets)