Hi,
My name is Madalin and i would like to start a collaboration based on required tasks on this project. We worked before to create other projects like this that have now tens of thousands customers.
I would propose you a solution linux based PPTP, L2TP and OpenVPN. One central server will serve for clients management, plans and NAS control, accounting, authorization and all requested services. Will use Centos or Ubuntu LTS as OS. Management interface will be php/mysql (+html, jquery) based and will use freeradius with mysql support for authentication and accounting.
We can implement solution with standard and custom plans, many NAS, unique ip or ip pool ranges assigned on each server, custom number of simultaneously sessions defined on plan of customer, traffic shaping with possibility to limit upload or download on each plan, possibility to assign custom servers on each plan or all servers for all users, sessions archive, connected sessions with possibility to kill any active session, quota support for each plan or customer, API support for Windows, MacOS, iPhone/iPad, Android apps... and many other custom options as would be requested.
If we can talk in detail about all tasks, hope we can start a long term contract with beautiful results for both sides.
Thanks.