am I really that far ahead...?
No, but for a different reason. You don't need to build, or buy anything. All you have to do is learn the car. Mazda Miata uses what is known as symmetrical wishbones in the rear. Once you set the adjustments (cambers) to be identical on both settings per arm, and you copy that setting over to the other side, you will square (thrust angle 0) the car, because the car was designed that way. This requires two wrenches.
Now that your thrust angle is set, you will need to get two jack stands, and a fine (the thicker you'll use the less precise it will me) fishing string. Run the string parallel to the rear wheel/thrust angle/center line of the car. Set the front wheel to be parallel to the string (0 toe).
Do the same thing on the other side. As homework figure out how to set positive, or negative toe (front, and/or rear). Once you figure this out, alignments will become second nature to you.
Optional step (this one is probably unheard of in motorsports). There is a way to set/go back to/change alignment at the track using just a string without any jack stands. All you need is a PVC pipe or any other pipe that is 2 feel long. This is how it's done:
Once you set your alignment in your garage, you record the settings, using the pipe method. First, you run a string around the car in the middle of all wheels, as if you were wrapping a gift. Then you take the pipe and you stick it between the wheel (rear) and the string, right in the middle of the tire. The string will bend outward. You go to the other wheel (front), and you measure the distance the string deviates from the rim in both places. Do this for all corners, and write it down. Now you can go back to your alignment within seconds at the track, in case it changes.
Optional step 2. Setup multiple versions of your alignment at home and measure using the pipe method. Now you can play with your alignment at the track between each session within seconds, without doing any long setup work. Costs no more than $5 bucks and you outsmart the competition.
Before I knew what the Miata was like I was looking for a string "system", but once I looked at the car I realized putting those "systems" inside the trunk, and hood, seems completely crazy to me. Not to mention it does not have to be precise at all.
Other alignment science stands, so you need to read up how to prepare your car for alignment and etc. It's all on the forum. Just make sure to verify for yourself everything.