Design Order

I have, now, had a chance to read a decent amount in the wind-tunnel design book (~50 pages). The equations and methods used in the wind-tunnel book are starting to click with those employed in the introduction-to-flight book, cementing my general aerodynamic understanding. My parents and brother will be arriving in just over three weeks, and I am hoping to have a component designed and ready for construction by the time they all arrive -- thus the design-order question.

The test-section is seeming to be the most logical thing to start with, as, for the initial version, I won't require the ability to take precise measurements (provided I have, at the very least, a good idea of how to amend that shortcoming later). The next component that I would foresee us working on would be the diffuser, immediately proceeding the test-section, as doing so does not require knowledge of the target size.