It is the bearing holder that should be tested for rotation. I have updated the description to make it clearer.

This is something I have noted to fix and will come in the next version.

I have made several tests and the frequency where very close.

You can reuse the stock idler from Prusa which is a 20T smooth idler (no teeth). However, I can highly recommend to use E3D or LDO 20T toothed idler with this optional part: https://github.com/gregsaun/prusa_i3_bea... . The size of the flanges are smaller and this is more important than teeth to me.

Sorry you had difficulties with this part. I have taken note of that issue for future improvement.

Is the printer able to find the 9 points needed for the auto bed mesh leveling?

Mesh bed leveling is working fine.

Is it possible to do XYZ calibration?

No this is not possible due to the different Pinda position. Some points cannot be mechanically reached.

Hahaha happy it was easy at the end. Curling the zip tie is a good idea (but not mandatory)!

fixed, thanks!

It is not, the MK3 and MK2/2.5 have the motor positioned differently. This is an image of the MK3 but the same orientation applies to zip ties.

The screw are self threading into the plastic. This will be more than strong enough to hold the screws and push the rod. It also avoid the screw to get unscrewed due to vibrations.