Just bought and setup the m5 but setup in access point mode until I know I am able to run a dedicated VPN router behind the m5.

I run a linksys router with dd-wrt (192.168.1.1). Connected behind this router is another dd-wwrt that is setup and running openvpn configured for ipvanish (192.168.2.1 but I access web configuration using 192.168.1.4). I run a computer wired to the VPN router, and computers wired to the main router. All computers on the main router are able to see and access shares on the VPN router. There are some I followed a guide to set this all up because I only know basic networking.

I want to put the m5 into this and use as my main router but not sure it's possible or way beyond my knowledge. Can I just alter configuration on my existing main router so it no longer works as dhcp server and just plug it into the m5? There are a bunch of firewall rules on the router that I assume allows the VPN traffic through. There is also bridge setup on networking tab that I really don't understand.

I'm way out of my skill level and understanding. I suppose I could just make note of all configuration and experiment with settings but thought I would post to see if anyone has a simple solution.