An Unknown Error Has Occurred...

...but I need roaming to reach other end of home (ethernet to the WAN port of the TC, then setup as Extended...aka bridge...results in error-see above).

In a roaming network configuration, the TC would NOT be configured for an "extended" network. Instead, it would be configured to "Create a wireless network."

The simplest way to set up a roaming network is to use the "automatic" method using the AirPort Utility. Select the option to extend using a wired connection. If you want I can provide you a step-by-step for a "manual" configuration.

Tesserax, I found your support post from 2013:

The good news is that the basic roaming network setup is the same with the new 802.11ac base stations, but you did discover that the Apple Support article is a bit dated (YES- Come on Apple, please update the PDF). I would expect them to update it soon.

In the mean time, let me try to give you some step-by-step instructions using the 6.x version of the AirPort Utility. First, there are a few key elements to successfully configuring a roaming network, and they are:

• All of the base station must be interconnected by Ethernet. Note: You can use non-Apple routers in this type of network.
• All base stations must have unique Base Station Names.
• All base stations must use the same Radio Mode and Wireless Security Type/Password.
• Each base station should be on a different Radio Channel. Using "Automatic" works well here.
• All base stations, other than the "main" base station, must be reconfigured as a bridge.

Let's start with the "main" base station. This will be the one directly connected to the Internet modem:

• AirPort Utility > Select the "main" base station > Edit
• Base Station tab > Base Station Name > Enter a unique name here
• Internet tab > Connect Using: DHCP
• Wireless tab > Network Mode: Create a wireless network > Wireless Network Name > Enter the desired name. This will be used on all base stations > Wireless Security: WPA2 Personal (recommended) > Wireless Password > Enter the desired wireless password. This will be used on all base stations.
• Network tab > Router Mode: DHCP and NAT
• Click on Update

For each additional base station added to the roaming network:

• AirPort Utility > Select the appropriate base station > Edit
• Base Station tab > Base Station Name > Enter a unique name here
• Internet tab > Connect Using: DHCP
• Wireless tab > Network Mode: Create a wireless network > Wireless Network Name > Enter the desired name. This will be used on all base stations > Wireless Security: WPA2 Personal (recommended) > Wireless Password > Enter the desired wireless password. This will be used on all base stations.
• Network tab > Router Mode: Off (Bridge Mode)
• Click on Update

So I did all this but one thing is the 2.4Ghz and 5Ghz wifi. How to handle that? (E.G. same SSID name or put SSID5G)

And DO plug from LAN ports of main base station to the WAN ports of the Roaming capsule and expresses?

Don't use Extended but Create Wireless "with same name" is the trick, right?

Thanks!

So I did all this but one thing is the 2.4Ghz and 5Ghz wifi. How to handle that? (E.G. same SSID name or put SSID5G)

All base stations MUST use the same SSID.

And DO plug from LAN ports of main base station to the WAN ports of the Roaming capsule and expresses?

That is correct.

Don't use Extended but Create Wireless "with same name" is the trick, right?

Correct.

THANK YOU!

Added a new Time Capsule, previous Airport Extreme. All have same SSID and pwd. Had to reset some iOS device Network settings to take the new but all good and working.

Hindsight: this link is best I found... http://support.apple.com/en-us/HT202056