Hello @ReeXNeeX,
We agree with @MartinLangmaid approach to using VLANs & Captive Portals.
We have many client locations using the Balance One with another manufacture WAPs (not preferred though it is what it is), and we successfully tie an SSID to a VLAN in the Balance ONE so that the device has to go through the Captive Portal to get connectivity.
InControl2 is used as the management platform for our customers as it is able to allow the Captive Portal to be linked in to many more options and is a lot easier to setup, monitor and administer than doing on the router itself.
Can we recommend you have a look at this previous reply in another post, this will cover almost everything you need to get started.
Happy to Help,
Marcus 