ERP Accounting Module Development

I need the first module of a new ERP built with a clear focus on accounting and finance. For this initial release, concentrate only on the features below so we can validate the core before moving on to sales, purchasing, and inventory.

What the module must do
• Create and manage invoices, record payments, and keep accurate customer balances in real time.
• Provide a secure customer portal where each client can log in and download their invoices as PDF.

Technical expectations
I am flexible on stack—Laravel + Vue, Django, .NET, or any modern framework that delivers clean code, an extensible database schema, and a straightforward REST or GraphQL API. Please include authentication, basic role permissions, and responsive UI layouts so the portal works well on desktop and mobile.

Deliverables
1. Fully functional web application covering the two bullet-point features above.
2. Source code in a private repository with clear commit history.
3. Setup and deployment instructions that let me reproduce the build on AWS, Azure, or a standard VPS.
4. A short user guide for staff and customers (PDF or Markdown).

Future roadmap
Once this accounting core is stable, I plan to add expenses, supplier bills, sales orders, purchasing, and full inventory management. Designing the codebase with modularity in mind will put us in a great position for those later phases.

Show me examples of similar finance-heavy apps you have delivered, outline your proposed tech stack, and estimate the timeline for this initial module. I’m ready to start as soon as we align on approach.