I really like the idea of the square pool with half time and finals...lots of chances to win. Only problem with that is you need to fill 100 boxes. Any other type can technically run with any amount of people.
Well with any squares pool you'd need all the boxes to be filled in otherwise you run the risk of a winning hit on an empty box.
But the thing is (as long as everyone agrees beforehand) the box buy in can be somewhat static. So, for example, you say the buyin is .1BTC/box. If you only get 10 people, now the price is .01/box and everyone has 10 boxes. If you only get 25 people, everyone gets 4 .025BTC boxes. Ect ect. If there end up being a non-even number, have the last ones to send get partial refunds. So, for example, if you only get 40 people, it would be .0333333BTC/box. The first 20 to send would each get 3 boxes and the last 20 to send would each get 2 boxes and .0333333333BTC refunded.
Just an idea.
I like that idea...and it gives most chances to win.
Will see how much interest we can draw...I will update OP soon.