Is there a designated place for a school group to eat their lunches?

Plenty but be aware for a large school group it may be tough because it's so open. There are stations but it's hard to keep track of a group of kids. Just my 2¢

Yes plenty of room

There is plenty of seating in the cafe area. Ask at guest services when you set up your field trip where they'd like your group to go.

Yes, contact guest services in advance