Ok. I asked a milling supplier, other milling machine users and even a company dealing with compressed air systems.
The knowledge flowing from it is hopeless, Everyone says something else. One says 100l tank another with 500l.
So I find the recommended compressor from the company Dürr Dental.
Here
https://dlc.duerrdental.com/download/Compressed+air/Compressors/Duo+Tandem/2582732.dd But this one is really expensive.
I decided on GENTILIN CLINIC DRY 3.50
http://www.gentilincompressors.com/en/product/clinic-dry-350 What do you think ?
PS i dont have pleace for bigger compressor and it need to be silent