The toughest part for me was figuring out how to cut long (6' +) straight lines in silnylon. Its pretty difficult, since its such a slippery material. I used a long straight edge, but the material kept slipping under it. I tried spraying silicone on my straight edge to get a better grip on the material, and it still slipped. I never came up with a perfect method. But the best in the end, was skipping the rotary cutter, and using a dry erase marker to mark my line and then cutting very patiently by hand. I'm going to try to figure out a better system for my next silnylong tent project.
I'm getting a tight enough pitch. If I don't guy out the back sides (you can see in my picture) it doesn't pitch as tight as I like. However, when I guy it out it pulls out my net tent as well (they are attatched at those points - just like Ron's design) and I get a lot more interior space. So, its worth the weight of a little extra line to be able to get the larger interior room for me. Plus, I get a great pitch that way.
The way I understand it, caternary curves are almost always good to have if you have a long straight ridge of material only supported at either end, but they would seem a little complex (at least for me) to integrate in this design. As you mentioned, the back and "sides" are all one piece, but the two front panels are separate sewn on pieces. So you could incorporate a caternary curve in those pieces, but There would be no way to incorporate it in the back three "ridge" lines if that makes sense. Unless you cut them apart and sewed them back together with a curve.
Hope that helps. Good luck, it was a challenging (again, for me) project but was really fun!
One other comment, I copied my hood design exactly from a camp-mor poncho tarp b/c I loved how it fit me, and the hood works pretty good on my cape.