I'm very experienced with this. First, the party is the most important part of the season. Send out a notice the minute you get your game schedule that it will be after the game at whatever location you decide. Don't ever ask for advice or "is this day okay".
Second, when you're choosing kids for your team, it is important to choose at least one kid with a big house, a pool, whatever. They get the party.
Third, if you find yourself in your current situation - nothing fixed - delegate. There has to be at least one annoying bossy parent on your team - give the job to them. And make sure to tell everybody that the job has been given to that person.
Fourth, the unwritten rule is that anyone who disagrees with your party plans doesn't come and doesn't have any say in anything. NEVER let someone influence you. You have the power - use it. Even if only one other kid shows up who can't even eat what you're serving, it's still the official end-of-season party, and you send out the party pics to everyone whether they were there or not.
Happy end of season!