Since it was raining last night, I ended up redrawing my front porch plans to reflect the actual measurements. I made a couple of changes (like using 2x6 framing), and the actual measurements were a little bit off.
The problem is that the original plans used stock windows that have specific measurements for the rough openings, so I had to readjust all of the internal framing. This ended up taking several hours, since the measurements are only available in four-inch increments, and the measurements were only off by an inch or so.And after all was said and done, I ended up with exactly the same windows I originally had, but changing the interstitial framing.
What it means is that the interstitials will be a bit more complex. For instance, instead of 2 2x6's nailed together to form posts, I have to create a kind of engineered lumber using plywood ripped to 5-1/2" widths and glue-laminated to the sides of a single 2x6. On the good side, this does actually work to make stronger posts.

I also changed the lower window framing because of the 2x6 walls. Now the lower sills will be continuous 2x6's fit into notches in the glu-lam posts, which will essentially make the whole thing fit together sort of like lincoln logs. And I'm going to pre-drill holes for the electrical, because it's a hell of a lot easier to do that before you put the walls together than afterwards.

I found a little secret in my perusing of various how-to books. WIth the header above the windows and doors, since I already have to make the header out of compositing both dimensional lumber and plywood, the trick is to sandwich a piece of thin steel flashing in between the layers. It doesn't add that much weight, but because it's sandwiched and held in place, it can't flex and it's incredibly strong-- you're essentially making a steel beam. And that's just cool.