3 yo bday party… catering help!?

Hi all

We are hosting a party for our 3 yo and we got much more rsvp than expected… most of her daycare friends are showing up plus siblings now we have maybe 25 adults and 30 kids lol

It lasts from 1030 to 1pm so obviously we will provide lunch but i have no idea how to portion the food. We plan to go to costco for sandwich platter + pizza + some snacks like cookies + drinks / water / milk

Anyone have any idea how many people we should aim for, people keep telling us a lot of the parents wont eat that much.

If you have any idea please let me know. Its our first time we feel overwhelmed!