The guide is the starting point. Yes.
I dont remember the details, but putting the pieces of information together answers the question: The built was done without IPv6 support, and this is what is used for the official builds: https://downloads.openwrt.org/releases/18.06.0/targets/ar71xx/generic/config.seed
I dont remember it in detail, but there was not more than smth like
git clone -b openwrt-18.06 --single-branch https://git.openwrt.org/openwrt/openwrt.git
cd to subdir
wget https://downloads.openwrt.org/releases/18.06.0/targets/ar71xx/generic/config.seed
./scripts/feeds update -a
./scripts/feeds install -a
make menuconfig (without changes to the config above)
make
I think the jumping point is the initial config.seed I took, which is (as I mentioned initially) most likely without the IPv6 stuff.
Interesting, I asked for the same just a few hours before, but in regard to ath79: Ath79 LEDs -- now GREEN (at least for Archer C7 v2)