Having excelled as a DevOps Engineer for more than half a decade, I am well-versed in Linux system administration and have extensive knowledge of various open-source solutions, which is perfect for your project. To cater to your needs, I plan on using FreeRADIUS as it's renowned for its robustness, scalability, and its seamless integration with different NAS devices like Fortigate. Leveraging my skills in scripting, setting up the voucher management system with data limits of 500Mb and 1000Mb will be a breeze.
Additionally, my experience managing users and devices efficiently aligns perfectly with your stated requirements. From creating and managing usernames/passwords to favorable user quota settings and even including a role for your desired account manager — I've got you covered. Furthermore, being adept at configuring Fortigate routers will ensure a smooth connection between the VPS and router.
In conclusion, my deep DevOps understanding, coupled with prior experience in systems similar to yours, make me the ideal candidate for your project. What sets me apart is not just my technical skills but also my commitment to delivering results that exceed expectations. Let's discuss your project further.