modular x-carriage - next level: MGN12 linear guide x-axis

As a new upgrade to get the tevo tarantula and my dual-hotend-setup ( https://www.thingiverse.com/thing:2172765 ) working on full bed size I made a decision: redesign my x-axis.

This contains a MGN12 linear guide.

To get it working with this higher position in comparison to the bottom edge of the extrusion, at least you have to use a 4mm-dropped module (v4-version), better 8mm (V5, read more at the end of the description).
Due to the no longer used wheels on the carriage it is possible t