I think due to the "draft" nature of this with only 1 card available, there's no real need to ban cards other than those already mentioned - Ante Cards, Chaos Orb, and Falling Star.
With 8 players, no one will end up with a "super P9" abused deck...
The whole purpose of restricting cards is to keep them from breaking a game, in highlander when only 1 of (insert cardname here) available - they aren't going to be completely abused. And everyone has a pretty fair shot at a lot of cards - you are at most blocked from 7 cards... after that - you have a shot at any one of them. And if you pick 8th - you actually have a great advantage as you can pick combos without having any interference since you get 2 picks in a row.
As far as the "sideboard" - did you mean that every unselected card is part of a collective sideboard - which your only limitation is 1 per deck? I figured the sideboard would come from your unused cards...