Are you going to prorate the added money with less than a full field? Nothing will tick off the players more than traveling to it to find out there are 63 players instead of the required 64, so there is no added money. I've seen it happen before.
Might also want to state what rule format you will be using.
Major point, Neil!
And of course you know the more added money the more attractive it is to players from outside your local region.
The highly successful Lafayette tournament has 128 players and races are to 7, FWIW. One of the biggees is their HUMONGOUS CALCUTTA (player auction).