Hi Jonathan,

This would work well and I've considered something similar my self but space is my ruler so decided 150x150 steel box section filled with sand is better for me. I've actually got the steel it's cut and waiting just need time now but there will be a thread created when build starts.

Regards your questions then here my opinions/suggestions.
#1 You need to clarify what you mean by carriages.? Do you mean carriage plates the bearings fasten to IE: Plates which carry Z axis and run along gantry.? (this would be classed has X axis on fixed gantry)

#2 Do you mean 100mm Z axis not 10mm.? Either way then DONT use unsupported rail of any kind.
Supported round rail is the minimum and really if your after a monster machine then you want profiled linear rails.

#3 See above but if you only had enough for one axis then make it the Z axis has this is the most important has it takes all the cutter forces. Next would be the moving table (Y Axis) but Again really you want profiled on all axis for a proper machine.
15mm rail would work ok but 20mm would be better has the bearing blocks are larger and will give better support, use the wide type for moving table has they give best mounting and support.

#4 Front face

#5 Nope not me sorry but I'm sure you'll easily get upto 1.5mtr or so before it's own weight starts having an affect. There will be some specs somewhere that shows it I'm sure.

Here's some other things to consider regards Cutting Ali.
The 2.2Kw spindle won't cut great big lumps with larger cutters so if your wanting to shift large amounts of material with larger size cutters (above 8mm) then you'll need more HP/torque.
Also you want flood cooling so work that into design, you'll need to seal concrete.!!