Comprehensive Business Management System Development

I need a customized business management platform that integrates multiple functions to streamline our operations. I run a non-profit and using multiple platforms everyday is annoying.

Key functionalities include:
- Managing customers, leads, and sales
- Overseeing volunteers, their tasks, and daily operations
- Handling invoices, expenses, and complete inventory system
- Tracking meeting minutes
- Voting on assistance applications that are filled out online
- Accounting and inventory management

User Access:
- Managers: Full control over all aspects
- Staff: Limited to managing their own tasks and records
- Customers: Access to view their information and requests

Ideal skills and experience:
- Proven experience in developing complex management systems
- Strong understanding of business operations
- Expertise in user access control and security
- Ability to create intuitive user interfaces for different user levels

There are other items on the wishlist we can discuss.

we can discuss further. I am looking for something very specific.

Please provide samples of similar work done.