Posted December 5th 2016
Getting this to work was surprisingly rough. I ran into trouble with OpenWrt versions, broken old config and interface name confusion. But it's nice now that it works.
The current (2016-12) stable version of OpenWrt is "Chaos Calmber 15.05.1". That version has support for v1 and v2 of my access point, but not v3. According to one page I found, you can hack (by editing one byte) the v2 image to install it on a v3 device, but that seemed too risky. I installed a daily snapshot from a few days back instead.
I did the install via the CLI, using 'scp' to copy the file to /tmp and 'sysupgrade' to do the install.
Snapshots don't include LUCI, the browser UI. So I installed that with 'opkg update' and 'opkg install luci'.
Both before and after upgrading, the wired interfaces on the access point worked fine but the wireless was 'disabled' no matter what I did. I couldn't figure out what was wrong and ended up re-installing the firmware via LUCI and unchecking the 'retain settings' box. After that, wireless worked.
Mostly for fun, I set up an unencrypted guest network alongside my regular network. I did that entirely in LUCI. I put it in its own network, 'guest_nw'. To get that talking to the outside world, I had to add forwarding to the 'wan'.
I also installed 'SQM QOS', i.e. 'opkg install ...' and limited the bandwidth for the guest network. It's a bit tricky to figure out which 'interface name' relates to which wireless network, in my case it was 'wlan0-1'.