I did it. I brought my cheapo hammock and DIY suspension system into the woods to test out and it worked! It took literally under one minute to hang, and it supported my weight very nicely. One of the carabiners I had in the setup got slightly bent from the strain, but that's because I wanted to see if one of those cheap dollar-store biners would support my weight. It did, but I wouldn't trust it on a camping trip of course.
Regrettably, and as rightly predicted by many here, it was too short a hammock (only 8.5' long) and a little too narrow to permit much of a diagonal lay, but I got a sense of what a properly sized hammock would feel like and I think I'll eventually be hammocking myself. My wife tried it out too; she's 5' 5" and 120lbs, but she too found it a little short and narrow. Shoulder squeeze would make this an uncomfortable hammock to sleep in. There was also the problem that this hammock was not made from one solid piece of fabric, but three long, narrow pieces sewn together. This means there are two quite firm seams running in parallel the length of the hammock which interfere with lying on the diagonal.
Nevertheless, proof-of-concept was achieved. The suspension setup worked, was easy to adjust, including the adjustable structural ridge line, the whole thing went up in under a minute and came down and was put away in about 2 minutes (no tarp, involved) and I really got a feel for what it'd be like to sleep, sit and lounge in it. And it didn't cost me a penny in materials.
So...now I have to think about if I want to make a properly sized one from ripstop material or instead buy a professional model, such as the Hennessy Expedition Asymmetrical Zip or one of the Warbonnets.
Anyway, thanks yet again to all who offered their expertise in my little experiment.