Robust SaaS Retail Management System Development

I am looking for a developer/team to build a complete business management SaaS for a retail shop.

The system should manage the entire business from one dashboard, including:

1. INVENTORY / STOCK

- Add, edit and delete products
- Product categories and subcategories
- SKU/product code
- Purchase price and selling price
- Stock quantity
- Low-stock alerts
- Stock-in and stock-out tracking
- Supplier management
- Purchase history
- Stock adjustment and damaged/lost stock tracking

2. SALES / BILLING

- Create invoices/bills
- GST billing support
- Barcode/QR scanning
- Discounts
- Returns/refunds
- Customer information
- Payment methods: cash, UPI, card, credit
- Printable/shareable invoices
- Daily/monthly/yearly sales reports

3. PROFIT & LOSS

- Automatic calculation of sales, purchase cost, gross profit and expenses
- Net profit/loss reports
- Product-wise profit
- Daily, weekly, monthly and yearly reports
- Expense management
- Cash-flow tracking

4. TRANSACTIONS / ACCOUNTS

- All incoming and outgoing transactions
- Customer credit/udhaar management
- Supplier payments
- Receivables and payables
- Payment history
- Cash/UPI/bank transaction records
- Automatic transaction entries from sales and purchases

5. CUSTOMERS

- Customer database
- Purchase history
- Outstanding/credit amount
- Payment reminders
- Customer-wise reports

6. SUPPLIERS

- Supplier database
- Purchase history
- Outstanding payment tracking
- Supplier-wise reports

7. EMPLOYEE / STAFF MANAGEMENT

- Employee profiles
- Attendance
- Salary management
- Roles and permissions
- Admin/manager/staff access levels

8. DASHBOARD
The main dashboard should show:

- Today's sales
- Today's profit
- Total stock value
- Low-stock products
- Expenses
- Outstanding customer payments
- Supplier dues
- Cash/UPI/bank balance
- Sales and profit graphs

9. REPORTS
Reports should be exportable to PDF/Excel/CSV:

- Sales
- Purchases
- Stock
- Profit & Loss
- Expenses
- Customers
- Suppliers
- Transactions
- GST-related reports

10. TECHNICAL REQUIREMENTS

- Modern, clean and easy-to-use UI
- Mobile + desktop responsive
- Secure login
- Role-based access
- Cloud database
- Automatic backup
- Search and filters
- Fast performance
- API-ready architecture
- Scalable so more shops/users can be added later

11. FUTURE SAAS FEATURES
I eventually want to turn this into a multi-business SaaS where different shop owners can create their own accounts and manage their businesses separately.

Please provide:

- Your previous SaaS/ERP/POS projects
- Recommended technology stack
- Estimated development time
- Development cost
- Hosting/server requirements and recurring costs
- Source-code ownership
- Post-launch maintenance/support
- Whether you can build the complete system rather than only individual modules.

I am looking for a long-term developer/team, not just a basic demo or template.