My family with some friends wants to have a outdoor gathering by mid April. Do we have to book the place earlier ? Can we order/bring cooked food from outside?

Large pavillions need reservation, but the small bbq don't. Regarding food, you can do whatever you want.

Booking Pavillions depends on day of week. The rules are on Fort Bend County website. See Google the park. General no first come during week , but check out the site.

You can order or bring cooked food from out side it just depends on what you want to do and it depends on the time and day that you book the place.