OpenVpn remote access with pfSense behind the ISP modem router

[ikonomn]

I need to create a OpenVPN remote access and this is my network
ISP MODEM ROUTER (makes the call to ISP and give me the dynamic public IP address)
PFSENSE BOX ( WAN interface IP 192,168.1.12 LAN interface 10.20.20.1/24) DHCP SERVER (10.20.20.20 – 100)
SWITCH
4 Dumb/Wireless Access Points ( fixed IP addresses )
I cant bypass the ISP modem router and take the public IP directly from WAN port so I take the private IP from LAN port to WAN port of pfsense.

How can I set up a OpenVPN to achieve a remote connection to my network (I run a java program to inform me by email changes to public IP) so I can remotely manage my network.
Thanks.

[SteveITS]

@ikonomn most ISP routers will have a way to forward ports to an internal device (your pfSense) or set one as DMZ to forward all ports.