Jar Jar and Pippin are making some very valid points and If you are not careful you are going to waste a lot of euros.

You are over complicating the design around the spindle and underestimating the importance of precision required in surfaces, etc. The fact you haven't even considered or looked into Fixed gantry design or even understand how it works tells me that you haven't done enough research into what is required for the machine you require.

I suggest you STOP and go take a look at fixed gantry designs because it's the BEST design for the size of the machine you are planning to build.