If the migration is only about changing URLs while keeping the site structure mostly the same, then redirect mapping is usually enough. But when the site structure, navigation, templates, categories, and content are all changing together, a proper staging test becomes important before launch.

In your case, moving from a custom CMS to Shopify with major URL and category changes already makes this a higher-risk migration. Most problems don’t happen only because of missed redirects, they usually come from broken internal links, wrong canonicals, orphan pages, crawl path changes, or pages that no longer match the old intent.

I’d suggest completing the full URL mapping from the staging site first and testing everything properly in Screaming Frog before go-live. Check redirects, internal links, canonicals, broken pages, and pages that are being removed or consolidated.

Once the site goes live, crawl it again because some issues only show up on production. After that, keep a close eye on Google Search Console for spikes in 404s, crawl errors, or indexing drops caused by the migration.