I can answer both of the questions about the number you will get.
1) You will not know the number you will get until the initial drawing takes place. The initial drawing will take place after a certain time period to allow all of the Forum Members that are interested in getting a low number through the chance of a draw to get their low number.
2) If you have a higher number that you want and it is still available after the initial drawing(eg. initial drawing has 100 members that bought 150 exclusives), then anything over this initial 150-160 pieces will still be available to buy. You may then be able to trade your lower number for your number or possibly convince Dave to sell you your higher number. There is NO RESERVING a specific number.