We implemented and provide captive portal service for cafe & salon shop in Taiwan since 2014. This service based on:
1. DDWRT (Flash the firmware for supported router, such as TP-LINKWR740N.840N)
2. LAMP (we build this service in DigitalOcean.)
3. FreeRadius
4. Provide some function as <Login with Facebook>,<Share with Facebook> and <LINE@add me>
If you want to test our service, you can prepare a router,flase the DDWRT firmware, and connect our server to test!
Based on our experience, I think we can achieve your project.