Pretty noobish router questions

[robertoisrad]

So the install guide has clear instructions on what to do with my router but I can't seem to make it work. Any help would be great!

My Setup:
Cable modem > Router > Switch
(Comcast) (DGL-4300) (d-link 8port)

So all of the computers in my house are connected to the switch and everything is happy, I plugged the HDA directly into a free spot on the router and I can't seem to get stuff to work.

First I just plain out disabled the DHCP server on the HDA, which didn't let me access any shares or apps

Second I re-enabled the HDA DHCP server and disabled the router's, I restarted my computer and was not able to connect to any computer, router, or internet.

Lastly I enabled DHCP on both and it seemed ok, the problem I saw right away was longer address for apps but I imagine having 2 DHCP servers fighting is not a good idea.

The last thing that is important to mention is that my wife has to connect to a VPN to work from home. The only way I was able to do this was to add her to the DMZ on my router, Does Amahi support VPNs?

Also I imagine my problem would be amazingly simpler if someone had a router control module for my router...

TY for looking!