Hello again. Well, true to my intention of updating as I go along, I'd like to express my current thinking on the whole project.
You'll be dissappointed to hear that now actually I'm thinking more of making a longtail, plus a two-wheel trailer. It would be better for my intended purpose, I think. I could make a really nice-looking and solid xtra-cycle style rack with the red steel tubing I have from the baskets, and also I could weld the bike itself together, instead of bolting.
I'll keep thinking.