How to setup a Raspberry Pi as an access point with bridge and wifi with NAT?

Question

I follow link below for setting up RPi access point with a bridge
Setting up a Raspberry Pi as an access point - the easy way

I install cloudstack manager which has cloudbr0 bridge
Now I want to have access point but I need NAT to isolate it from router
So the topology should look like below
What should I change for such configuration?

                               RPi
               wifi   ┌──────bridge──────┐   wired            wan
mobile-phone <.~.~.~> │(wlan0) br0 (eth0)│ <-------> router <-----> INTERNET
            \                   |                   / DHCP-server
      (dhcp 192.168.4.x   (dhcp 192.168.50.x      192.168.50.1
       from RPi)           from router)