I managed to get RoPieee working. Thanks for providing it!
I did not get my wifi adapter to work, though, using the web interface. SSH-ing into the Pi and running
sudo pacman -S netctl, creating a config file, and
netctl enable did the trick. (as per wifi configuration on arch)
But now I wonder: will this remain working after there is an update to RoPieee? And would this be something that can be added to the web interface? (for other users like me)