Chris, does “completes seed” mean when the torrent’s status changes to Seeding: 2? It could be the same guy, though.
Betting: yes! Even personal P2P where one of the sides decides (because in this case the betting persons likely know each other, the process can be simpler than with unknown parties).
I think it would be interesting if contestants used existing UIs (if they find that advantageous, of course) such as Counterwallet (source), Indiesquare Wallet (source), Tokenly Pockets (source), etc.
I may edit this post this weekend, in order to add more without creating too many separate comments.