If the router has a hotspot section then you don't need to further upgrade it.

If you want to use a password to protect the wireless network then you can configure encryption. In the router's admin click Wireless-Wireless security and set however there certain wireless encryption protocols are known to be unsecure. The most secure encryption you can use is WPA2, but is still susceptible to known attacks. When using DD-wrt, WPA2 seems unreliable, so use WEP.

You can find the splash page's URL from the control center. Click manage-locations-name of location- VIEW HOTSPOT FRONT PAGE and copy the page's URL.