Technical SEO audit for a Shopify store

Plum Street Studio runs a homeware Shopify store with about 800 products. Organic traffic has been flat for a year and we suspect technical issues: duplicate collection pages, slow templates and a messy internal linking structure. We want a full technical audit with a prioritized fix list: crawlability, index coverage, structured data, page speed and internal links. Deliverable is a working document our developer can execute on, plus a 1-hour walkthrough call. Bonus points if you have Shopify-specific experience and can name the usual template pitfalls.