Heyho 
,
Are there any practical insights or recommendations regarding the calibration or benchmarking of the CNC machine? Perhaps tips on proven .stl objects for evaluation/benchmarking purposes? I would be very grateful for your suggestions.
Best regards 
Hey there,
Well in terms of calibration or benchmarking your CNC, I think the most important thing is to check whether your CNC is square. Make 4 dots on each corner of your spoilboard, with the same distance in X and Y direction. Then measure the diagonals. They must be equal. If not, you need to adjust one the Y ball screws until you get exactly same diagonals.
Other than then, you could also check the rigidity that you got, just like shown in the video in order to evaluate the build quality of your CNC.
As for some kind of model or object, you don’t need anything special. Just do some test by cutting let’s say 20mm square, and another of it at 45 degrees, and measure the dimensions.
Cheers,
Dejan