I've set up a few of these at my local bar and at the legion. I've never seen anyone have a set number of squares that must be sold, the establishment has always taken all the squares not sold by gametime. If you're running one privately, it's probably a good idea, unless you want to gamble large.
As far as payout goes, 50% for final score, 25% for halftime and 12.5% for first and 3rd quarter is pretty standard (assuming you're talking football). Some people add a reverse final score but I've never bothered with that.
This one will be final score payout only. Winner take all. Never done them before, and haven't picked a game yet. I need a set number of squares to be sold though for reasons I think you can deduce. lol
Understood
It's your show, run it your way or dump it...but you have the right mindset...cover your ass!
One thing you should consider....if you sell half and noone has the winner, who do you pay?