A 20kg (44lb) load cell should do nicely for testing. You can buy them pretty cheap ($15-20) off Ebay. The sparkfun amplifier should work fine.
Creating the contraption that mounts the load cell is the fun part. There are many ways of doing this - just make sure it's strong and sturdy. In any case, a good design can always be up-scaled to suit a larger load.
I almost can't believe that it was 15 months ago that I started this post. I'm still mucking around with writing software - the basis is using an Arduino development board - that project started in June 2015. More than two years back. With the software and data acquisition, I've taken a different approach.
My software can be used to record data (via a tethered device) or can import data from other devices, and export files. Recording and analysis is all done in the same window.
I'll report back in another two years when it's all finished.