A Shopify store is quick to open and slow to correct. The decisions that decide how well it trades are made in the first fortnight, before anything looks like a website.
The first is the catalogue model. Shopify keeps a deliberately narrow product structure, so a range described by size, colour, length and finish has to be resolved into options, separate products, or metafields before a single row is imported. That is not a styling question. It sets what can be filtered, what can be reported on, how stock is counted and how painful every future bulk edit will be.
The second is the template set. A store needs homepage, collection, product, cart and account templates that hold up against the catalogue you actually have, including the ranges with two photographs and the products with forty variants. Demo catalogues hide exactly the cases that cause trouble.
The third is operational. Payment providers, tax registration and rates, shipping zones and rates, notification wording, staff permissions, order tagging and the apps allowed to touch an order. None of it appears in a design review, and all of it appears in the first week of trading.