First steel diy CNC router build

[ivars211]

I will start by saying, that this is my first ever CNC design and build, so any critics and suggestions are much appreciated. General idea from here.
Before I start welding, I want to make sure my desired design actually is any good.

So overall description:
Steel frame contains from 100x50mm box sections, 40x40mm intermediate supports; 50x50mm for granty and another 100x50mm in the bottom for locknut. Z axis is built from 20mm aluminium.
Y axis - 900mm SBR20 supported rails (distance between rail blocks outside-to-outside 250mm)
X axis - 700mm SBR20 supported rails (distance between rail blocks outside-to-outside 200mm)
Z axis - 400mm SBR16 supported rails (distance between rail blocks outside-to-outside 200mm)
RM1605 ballscrew for all three axis. Buying complete set from Chai.

For electronics, Nema23 3Nm (425oz.in) should be enough to move this beast around. Buying complete set from here.
Chinese water cooled 2.2kW spindle from ebay as well.

This CNC will be mainly used to mill/cut/drill aluminium. Preferably with air coolant, to get rid of chips.
Like I said above, please fill free to comment on any mistakes in design.

Thank you.