You have every right to pick and choose your players based upon any criteria that you feel fits the situation and what kind of game that you want.
I started my first Pathfinder game recently, and I'll admit that I picked the group based upon several considerations. The first being posting reliability... Most group games fall apart because a player, or players, drop without warning after it has begun and that can cripple a game. So, if I see a regular posting routine, that's a plus. Next is if the character fits the game. If you get more than one of the same type, do you need two sorcerers, for example, or does a character fit the concept that you have.
Then, there are players that you just don't want to involve in your game for whatever reason. Fortunately, I didn't have any of these, but I'm not concerned about telling someone that this may not be the game for them, or that their character concept doesn't fit the setting. As someone else said, we are (We must assume) adults and can take rejection. The "not on a first come/first serve" statement helps too. It actually does encourage more players... just put a time limit on it or you'll have people promising to get a character in and wait until the last minute, or you'll be waiting so long that you start to lose players.
Whatever you do, you have the right to hand pick your group.