Google scripts shopify integration ERP

I run a custom-jewelry business and have a working ERP built on Google Apps Script bound to a Google Sheet, integrated with Shopify (order webhooks + Admin API). It's live in production, roughly 1,000 orders, 40 script files, a test suite, and handles order intake, deposits, fulfillment, manufacturing tracking, and commissions. I'm NOT looking for a rebuild or a new platform. The system works. I want an experienced second set of eyes before I take on the next phase, and if the review goes well there's a larger build to follow. Scope: a written review covering four things Webhook reliability. Orders arrive via Shopify webhooks. Where can events be missed, duplicated, or processed out of order, and what recovery/reconciliation gaps exist? What would you add (dedupe, retry handling, periodic backfill)? Scaling risks. As order volume grows: Apps Script 6-minute execution limit, daily quotas, LockService contention, sheet-size performance. Where does this architecture start to hurt first, and what are the cheapest mitigations? Shopify API usage. Review how the code calls the Admin API: scopes, API versioning, pagination, rate limits, error handling. Flag anything fragile. (For context: we recently hit an issue where orders older than 60 days silently returned null because the app lacked read_all_orders. I want to find the rest of that class of problem before it finds us.) Architecture for the next phase — this is the important one. Today, Shopify is the source of truth and the ERP syncs FROM it. The plan is to invert that: the ERP prices and builds orders, then PUSHES them to Shopify. I want your recommended design for this — draft orders vs. order creation API, how to keep the two systems consistent, failure modes, and what in the current codebase needs to change to support it. What you'll get from me A zip of the full codebase (sanitized: staff comp and customer PII removed, everything else intact) A sample workbook with the real sheet structure and anonymized data at real volumes The store domain and context on the business flows; API credentials only if/when we move to a build phase Deliverable & terms A written document (however you like to structure it) covering the four areas, with findings ranked by severity and a concrete recommendation for #4. I'd suggest a capped engagement of 8–12 hours. tell me if you think the scope needs more or less. Happy to do a short call first if useful. Does this fit what you do? If so, send me a rough estimate and I'll get you the files.