Printing with custom QTR "profiles" is totally different than the way you print color images with a custom ICC profile with photoshop or lightroom controlling the color/tonal adjustments. When the instructions to make ICC profile say to choose the printer/ink settings you want to use for printing the step wedge it means the output dpi, photo or matte black, dithering algorithm, and the mix of the different tint curves/profiles for the given paper.
This can be a confusing subject to discuss because both methods refer to "profiles," but are actually used in completely different ways. Print "tone" is also hard to talk about because in the darkroom we used different papers (warm tone/cool tone) or "toned" the prints with selenium, sepia, etc. to change the print color. When making digital prints "tone" can be talked about as ink density as well as print color.
When discussing QTR I prefer to think of the ink profiles for papers and the tint/color as a "Curve" and the ICC profile only as a soft proofing tool that will approximate the tone (density) and color (tint) for the "curve(s)" used to print the target.
If you are using a paper that has pre-made curves for your printer included with QTR, then you can print the test target with the curve (or a custom blend/combination of curves), measure the target with the photospectometer, and then use the ICC creation tool to make the softproofing profile.
I would actually suggest printing the 21x1 step-wedge multiple times with only one curve each time to see what each one will look like. I would then test a few different curve blends to see what tint will suit your preferences. Then print the 51 stepwedge target with those desired settings and use the ICC creation tool to build the profile for softproofing.
If you are not using a paper that has pre-made curves you will need to build your own, which is relatively easy once the process is understood. Then you do the same as if you had pre-made curves—print the stepwedge with the desired settings, then measure and use the ICC creation tool.