I am wanting to build a 5' by 15' grid to create 27 18" square openings so students in my school can display 16" square paintings in our Media Center. I am planning on using 1x2's for construction, and I will use my Kreg jig to assemble everything.

Because I am working on a budget, I am hoping to use pine. But, is pine going to be stable enough to keep everything from warping or twisting? All of the verticals will be 57" tall, and the horizontal dividers are going to be 18".

Is poplar a better choice?