How does the draw for the play off round work? Are teams seeded or is it a random draw?
It's seeded-ish. The seeds are paired and then drawn into either the top or bottom half of the bracket. So the #1 seed and the #2 seed will have a random draw for that pairing to determine who is top half vs bottom half. Same for 3 and 4, 5 and 6, etc.
So if you finish 1st in the table you may end up playing the winner of 15 vs 18 or 16 vs 17 depending on how the draw works out. I'm guessing it's mostly done to minimize any collusion in the final match day.