How do i setup opnsense with a range extender?

[IvanBlim1nse]

Hello, I am trying to setup my OPNsense firewall with a range extender (which I want to use as a access point/router for opnsense) This is the layout i'm going for: (My phone line requires DSL btw) (I am running OPNsense on a VM in virtualbox too.)
Internet -> DSL Port on wall -> DSL Modem Router -> Unmanaged LAN Switch -> LAN card 1 (for LAN)
                                                                                                           | --> (both are in the same pc)
                                                                                                           -> LAN pcie card 2 (for WAN)
                                                                                                           | --> (Through the LAN port on the switch)
                                                                                                           -> Range Extender/Router (It can be used as an access point)

I want to basically use the range extender as a router for wireless devices and I want all the traffic to go through the OPNsense firewall. I also want all the LAN traffic going into the LAN switch to be redirected to the OPNsense firewall. I can't use my DSL modem router in just wireless mode as my house phone requires DSL from the router to function properly. Also, I want all the network traffic going through the DSL modem router (which is currently serving as a wifi router mode too) to be redirected to OPNsense's firewall. I also want any new devices connected to the LAN switch to use DHCP which is on the OPNsense DHCP server. How would I also setup the DSL Modem Router to not use it's own dhcp server, and use OPNsense's DHCP server? I'm a complete beginner also. I am also new to network security in general. I am 14 btw, so please don't mind the slightly bad english.