Simple Billing App for Print Shop

I'm looking for a straightforward billing web application for my xerox/printout shop. The app should be able to generate invoices and manage inventory.

Requirements:
- Functionalities:
- Generate invoices
- Manage inventory
- Daily Sale report
- Daily Cash & UPI to show seperately
- User Interface: Simple and minimalistic

- Device Optimization: Desktop and Mobile

Ideal skills and experience:
- Experience in developing web applications
- Strong background in inventory management systems
- UI/UX design skills for minimalistic interfaces
- Ability to optimize applications for both desktop and mobile devices

Please provide examples of previous work and an estimated timeline.