This was a good read. More of an account of your experience than a review but I'm not in the market for a cargo bike so I enjoyed it :)

Yes, don't leave us hanging!

This is a great plan, sounds like it will be a lot of fun and you'll learn a lot. All the best and do post updates!

One more suggestion is to assess your riding position regardless of what stem you end up going for.

If you're always riding with your elbows locked out and your arms straight, your weight will be on your hands.

If so, think about riding with soft elbows, with your core taking the weight instead. This is overall more comfortable and more aero too so you'll go faster with less effort.