I did everything you mentionned, and I have a clean build.
very basic.
but still just some packages, but in my config I chose ''curl'' so I can use it.
root@OpenWrt:~# opkg update
Downloading https://downloads.openwrt.org/snapshots/targets/mvebu/cortexa9/packages/Packages.gz
Updated list of available packages in /var/opkg-lists/openwrt_core
Downloading https://downloads.openwrt.org/snapshots/targets/mvebu/cortexa9/packages/Packages.sig
Signature check passed.
root@OpenWrt:~#
here my ''feeds.conf;
src-git packages https://git.openwrt.org/feed/packages.git^f9ecc4344
src-git luci https://git.openwrt.org/project/luci.git^fb6e62e
src-git routing https://git.openwrt.org/feed/routing.git^ea4a3f2
src-git telephony https://git.openwrt.org/feed/telephony.git^4d2bb84
src-git freifunk https://github.com/freifunk/openwrt-packages.git^98e83ff