I have a similar setup, but with a switch in a different location.
I have a Comcast cable modem. It's IP is 10.1.10.1 and I have my DIR-825 connected to it. I set a fixed IP address in the DIR-825 to 10.1.10.80 on the WAN side.
The DIR-825 LAN is 192.168.1.1 on the LAN side and has DHCP starting at 192.168.1.100 and up.
I have a couple of wireless computers and laptops connected to it via the 2.5 Ghz wireless side.
I have a Gaming Adapter connected on the 5 Ghz side and have an XBox 360 connected to the gaming adapter. I also have an Ethernet Bridge connected on the 5 Ghz side.
Out of the ethernet bridge, I have a 5 port dumb switch. I have a computer, a satellite receiver, a second XBox 360, and Network Attached Storage drive connected to the switch. The NAS drive has a fixed IP address of 192.168.1.75.
I have a computer, a Windows Home Server, and a second NAS drive connected to the DIR-825 ethernet ports. The NAS drive has a fixed IP address of 192.168.1.75 and the Windows Home Server has a fixed IP address of 192.168.1.10.
Everything else on the network uses DHCP IP addresses from the DIR-825.
I have absolutely zero problems with this setup. The last time I looked, my link had been up for over 20 days with no problems.