I figured out where my math went wrong (at the very beginning).
I thought I needed the following:
6.66 board feet of 4/4 Poplar
10 board feet of 5/4 Quartersawn White Oak
20 board feet of 4/4 Quartersawn White Oak
After doing the math again, here is what I actually needed:
5bf 4/4 Poplar
20bf 5/4 QSWO (twice as much!)
24bf 4/4 QSWO (20% more)
Here is what I ordered (adding 50% to each):
10bf 4/4 Poplar (plenty)
15bf 5/4 QSWO (not enough)
30bf 4/4 QSWO (barely enough)
And here's what I should have ordered:
7.5bf 4/4 Poplar
30bf 5/4 QSWO
36bf 4/4 QSWO
I had some leftover 5/4 QSWO from a previous project which is probably the only reason I'm not paying another shipping charge for more wood.
So I got really lucky that I was able to fit all of these parts onto the lumber I had, and this is likely the reason it took so long to place all the parts. I think I've got less than 5% waste. :P Squeaky!