Adding a gargoyle router to an existing router

[riboswitch]

Hi, I have an Asus RT-N66U router that gives great WiFi connectivity for myself but I would like to provide WiFi internet to my neighbours and would like to set a data usage limit for their guest network. Since my current router does not support the gargoyle firmware (or so I've read on different forums), would I be able to create controlled guest wifi networks if I connect a gargoyle supported router to my Asus router? Would this be a LAN to LAN connection or a LAN to WAN? Basically how would I go about doing this?

[ispyisail]

LAN to WAN

and change the subnet

e.g.
router1
192.168.1.1
255.255.255.0

router2
192.168.10.1
255.255.255.0