Hello, I am looking to build a Windows desktop billing software named BILLING MADE EASY. Please go through the complete requirements below and share: Your estimated timeline Cost Technology stack Similar work experience (if any) PROJECT TYPE Windows Desktop Software Works on Windows 7, 8, 10, 11 Offline-first (internet optional) Single .exe application Local database (no compulsory cloud) USER ROLES & SECURITY Owner & Staff login Role-based permissions Full audit logs (invoice edits, number changes, FY overrides, cancellations) COMPANY MASTER Company name, GSTIN, PAN Address, contact numbers, email Bank details, UPI ID Company logo Used automatically in invoices, reports, PDFs, prints SALES MODULE GST & Non-GST invoices Auto invoice numbering Invoice number editable after save (Owner only, with audit log) Draft auto-save (power failure safe) Cancel invoice (do not delete, reverse stock & GST) Shortcut to view last 3 sale prices for same customer (on-screen only) PURCHASE MODULE Purchase invoices OCR bill scan (photo/PDF → auto draft → verify & save) Shortcut to view last 3 sale prices while purchasing QUOTATIONS Editable even after FY change Convert quotation to sale invoice Quotation remains unchanged after conversion Logical link maintained INVENTORY Product master with HSN/SAC Stock in/out Low stock alerts PRINTING & PDF A4, A5, Thermal (58mm/80mm), Dot-matrix Multiple invoice designs & layouts Preview before print Save as PDF COMMUNICATION Email (SMTP) WhatsApp Web / Desktop Official WhatsApp Business API (enable/disable) GST & REPORTS GSTR-1, GSTR-3B, HSN summary, ITC Sales & purchase GST registers Cancelled invoice GST reports Export to Excel / PDF / JSON Auto GST filing (optional, owner-controlled) E-WAY BILL Manual-assist mode (default) Official API support (optional) Generate / cancel / track CHEQUE PRINTING CTS-2010 compliant Multi-bank templates Alignment settings Cheque issue log MOBILE INTEGRATION Upload invoice photos from mobile via local Wi-Fi Attach images to invoices FINANCIAL / ACADEMIC YEAR FY-wise data separation Prefix/postfix change on FY change FY change confirmation 5-day grace period before FY lock Auto-lock after grace Quotations editable across FYs Hidden emergency override for locked FY (owner only, fully audited) BACKUP & RESTORE Auto backup (configurable interval) Maintain last 3 verified backups Delete old backup only after verification Automatic email backup Restore preview before applying UI / UX Very user-friendly Look & feel inspired by GoGSTBill (not copied) Clean, modern design Before login, login, and after login screens DELIVERABLES Working Windows .exe Full source code ownership Database schema Build instructions Please review and share your proposal.