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.