DIY with Chinese router kit

I am building myself a CNC based loosely on the Dremel CNC on Youtube. I decided to put a 300W Chinese router instead of Dremel (rpm, ER11 and a little bit more power). Now I am so far that I have tested drawing couple of lines with a pencil and it works.

I ordered myself a router kit over aliexpress a longer time ago. Until now I just looked at the collar and adapted my construction accordingly. Now I finally packed it out and noticed that it does not look that convincing. The power does not have a connector for the PE - is it safe (and a better idea) to connect the PE-wire anyway on the metallic casing?

Is the controlling of the revolutions with the potentiometer such a great idea or is it regulated somehow internally on the power unit?

I think that this type of kit is pretty widely used but I did not find anything specific for those two questions.
I also saw couple of Youtube videos where they used very similar CNC routers from China...