I place the order for the aluminium extrusions, it seems that something starts to happen with this build. :-)
Except for the higher noise level between air cooled VFD spindles vs water cooled spindles, is there another reason why not to take a 2.2kW Chinese aircooled VFD spindle? I found one aircooled with four bearings, shipped from Europe and the price looks good, to me.
I will post the link tomorrow when I get back home.