Started working on the bottle stack and a stand while waiting for some seeds to sprout:

Still have one more 1.5-liter bottle to add. I couldn’t find the eco-shape 1.5-liter bottles, so I just used straight-walled ones. Since they don’t have a waist to them, I put the 3″ net cups all the way down in them, which leaves room for a nice tall cutout (about 6 inches / 150 mm high):

Each bottle has two cutouts (on opposite sides) and each cutout is 1/4 of the circumference. Given the distance that the solution will have to drip from one cap to the net cup below, I may put in some sort of guide tube for each. Also need to make a donut-shaped plate for the top of the stand to center the bottle stack and possibly hang the bottles from if they want to buckle due to the weight of the media and plants.

Here are some additional details on the design:

-reservoir bottle is Deer Park Easy Pour 3 L (UPC 0 82657 33412 7)
-plant bottles are Le Bleu (lebleu.com) 1.5 L (UPC 7 34341 00019 0)
-net cups are HG3NETCUP 3″ (Made in China) (UPC 6 38104 00081 9) (bought on eBay)
-threaded rods are 3/8″-16 x 48″ L
-base is 3/4″ MDF, 8.5″ diameter with threaded rods and feet on 7.5″ bolt circle (reservoir bottle can be removed laterally between two of the threaded rods)
-rubber feet are 1″ dia x 1″ high (screwed on)