Ana's plan called for using 8 hinges (I'm not sure on the placement of those). I used a total of 16 to ensure sturdiness. I put two hinges on each corner of the 1x8 piece and a hinge anywhere the corners connected. I used Narrow Utility Hinges (1-1/2" Zinc plated). The pack of 2 cost $2.27 and comes with screws. My biggest regret is not painting the hinges before I put them on. I waited until after screwing them in and it was a pain and makes my paint job look sloppy.
Although I priced this build out, I ended up using wood I already had in the garage. I didn't have enough 1x3 to make the anti-tipping feet so I used a 2x4. I also didn't make the rounded edges, just a few angled straight cuts.
THESE ANTI-TIP FEET ARE A SAFETY MUST, DO NOT SKIP THEM!! I've seen a few commenters say they skipped the anti-tip feet, but for us they were a must. My kid would have easily knocked his tower many times if it weren't for these anti-tip feet!
Couldn't be happier with this build. Totally worth every penny. Hands down my favorite kitchen addition!
Wrote about this on the blog too: http://thehuth.blogspot.com/2014/11/ana-whites-little-helper-tower.html