Connecting an Airport TC to a Cisco Modem/Router

I have just moved and now have 5 people under one roof. So Im trying to figure out whats the best scenario. Our house will have up to 10 devices (Laptops, phones, Xbox, AppleTV.) all running on the same ISP at any given time. I have a Cisco DCP3825 modem/router acting as a modem & router, using IPV4 with WLAN @ WPA2 personal - AES. and DHCP is on. Its running on N only, at 2.4GHz. Then I have it connected to my AirPort TC in Bridge Mode via Ethernet cable in the WAN port. I am connecting in DHCP mode with 2 DNS servers. I created both a 2.4 and 5GHz channel in WPA2 Personal. I use my TC for Time Machine and didnt want to have to fight for bandwidth while backing up. Since the modem can output its own network, I figured I would make my own and use it just for my Time Machine backups, syncing with my iPhone and general use on my MacBook Pro.

Is this the best set up for the scenario tho. I guess my other options are to put the modem into bridge and Only use the AirPort TC. Or, I can make my AirPort TC extend the modem/routers current network. Keep in mind they are connected via Ethernet and sitting beside eachother on the desk.

Any suggestions and opinions are greatly appreciated. I just want to have the best range and signal quality possible while dealing with so many devices on it at once, all while trying to use Time Machine and AppleTV.