Sheets CRM + Inventory Integration

I need a single, streamlined system that ties our customer relationships and our stock movement together. My first choice is Google Sheets combined with Apps Script because it lets the whole team work in a familiar interface, but I am open to hearing a persuasive case for another stack if it delivers better speed or reliability.

Core scope
• Customer module focused on clean contact management: add, edit, search and archive contacts in one place, with every change instantly rippling through all linked records.
• Lead pipeline that shows real-time status tracking from enquiry to quotation and finally to won or lost, all on one visual board.
• Automatic creation and storage of quotations, invoices and follow-up activities, eliminating double entry.
• Integrated purchase, sales and godown inventory with live stock counts, low-stock alerts and an always-accurate product list that also feeds the website catalogue.
• Business dashboard pulling key sales, inventory and CRM metrics so management can act at a glance.
• Full automation between CRM, sales documents and inventory: one update anywhere should update everywhere.

Acceptance criteria
1. No duplicate data allowed; edits cascade automatically.
2. Low-stock alerts trigger without manual refresh.
3. All modules stay fully usable on desktop and mobile Sheets.

When you reply, please include:
• A link or brief on CRM projects you have built—especially Sheet-based.
• Your proposed tech approach (confirming Sheets + Apps Script or offering an alternative and why).
• Estimated timeline with key milestones.
• Fixed-price quotation.

I’m ready to start as soon as I can see a solid plan.