Autoscrolling only works with audio files. So if you need autoscrolling, just import the original song or one of your recordings and use that to timecode lyrics (you can encode that song with 64kBit to save space if you need to). Then set the song volume to -inf. This will mute the track but keep lyrics scrolling.
Unfortunately you can't assign key commands in the current MacOS version. I think I need to take a look at this as this limitation does not make sense really. In the meantime you can use bluetooth pedals or any midi device that has buttons. Something like an Akai LPD 8 or Korg nanoPad are not expensive and will work nicely.