Please clarify used technologies, because of you talking about VPN but then specify socks protocol as used VPN.
There are something wrong in definitions.
Also, due nativity you could not simple specify socks protocol for all apps, some apps will ignore that.
Next, please clarify area of this project, because of as I see you need at least 7 big parts here
1. Windows app, which will do work for congratulation instead of user.
2. Mac app, same as windows.
3. DB with users and payments
4. Management website to manage whole project
5. User website where they will pay and manage subscription.
6. Web-api part, to exchange with mac and windows apps
7. Controlling part, which will limit users to connect, Must be placed on your proxy/vpn servers to limit users, because of if you will place it on client side - it will be hacked and users will use your services for free.