There are lots of possible answers to those questions.

Lighter wieght leather is better, if you don't want a great weight. 2-4 oz./sq. ft.

Lamb is softer, smaller, takes more skins. Cowhide is harder, more durable, stretches less, less expensive, but not as comfy.

I can't answer the pleat question, as all the leather ones I have made were overlapping panels, and not continuous length material. And single purpose, too, to protect me from being burned in the forge shop whilst smithing.

Conditions it will be subjected to are an issue as well.