Spooktacular Creations Deluxe Dragon Costume Set with Toys for Kids Role Play

My boy is not yet 3.5 years old and he is 38lbs and 38 inches height. He is wearing 4T in normal clothes . What size will he fit in this costume?

Is there a zipper? My nephew is still in diapers and we want to be sure we can easily do changes.

For the 5-7 yr size, do the feet just lay over the shoes? I don't understand why they design the feet this way...they're going to get so dirty.

Our son is 18 months, 23 lbs. Which size should i get?