If you don't have access to a 3D printer, you can use a service like 3D hubs, makeXYZ and shapeways. Adafruit also carries 3D printers in the online shop. We suggest also checking your local library, makerspace, or school.
The frame is made in 4 identical parts. Print 4 copies of lightbox.stl. Orient it when you slice so that the latticed surface is on the print bed. You shouldn't need supports, although the USB breakout opening will require some degree of post-print cleanup.
The top acrylic panel is attached to the frame using 8 clips: 4 for the corners and 4 for the sides. Slice the side clips on their side so no support is required. Slice the corners on their tops and use support from everywhere so that where the panel sides in is filled with support material. It will need to be carefully removed after printing.
The final pieces are the clips that are used to hold paper in places. You will need at least two of these for the top of your paper, and if using a letter size or A4 paper, a couple on the bottom are a good idea as well.
You'll also need a mounting tray for the Feather board. You can get that from Thingiverse.