xfinity bridge mode to sonicwall firewall help

hi guys , i am a network student and this is my situation .,,, i want to connect sonicwall firewall nsa 220 to my xfiinity router and do dhcp through my firewall and wifi traffic going to a Cisco AP (already configure with 2.5 and 5 )connected to my sonicwall ,, so i can start playing with firewall rules, policies etc…. so will be like this Internet>>>Xfinity router>>>sonicwall >>>Ap .

Now,, do i need to put my xfinity router on bridge mode to disable dhcp on my xfinity router???
if , so.. my firewall WAN need to be configure with the router LAN IP gateway (10.0.0.1) or with my public ip ???
my new LAN dhcp pool on my firewall needs to have a diferent subnet like 10.0.1.1 or not ???

Thank you guys , hope you can help me understand this.