steel tube build concept - 1500y,1000x,250z

[outtastep]

photos are a bit all over the shop , this is the most recent version- most of the steel, like deck and y rails and gantry sides was to be 100x50mm steel maybe 2 or 3mm thick, with the gantry maybe 150x50. The X carriage is envisaged as a aluminium plate perhaps 10mm thick with lots of bearings either side, z bit aluminium plate made into a bit of a box. was hoping to get 250mm travel on Z. Gantry is 300mm above bed/ deck/base. Might be pushing it a bit with Z.
With the base i was thinking of 5mm steel plate. there is also steel plate in corners of and holding ball screw ends/ motors.

im a bit concerned with having this type of supported rail as i have read some bad things about the here, also probably not the best having them on their side as per my x axis ?
cheers ben