I think I figured YZ axis arrangement. Options:
Click image for larger version.  Name: 27-4 y20z15 fixed Y nut.jpg  Views: 3466  Size: 22.7 KB  ID: 27612Click image for larger version.  Name: 27-4 y20z15 fixed Y nut front.jpg  Views: 3484  Size: 25.2 KB  ID: 27613
and
Click image for larger version.  Name: 27-5 y15z20xLGW fixed Y nut.jpg  Views: 3469  Size: 18.8 KB  ID: 27614Click image for larger version.  Name: 27-5 y15z20xLGW fixed Y nut front .jpg  Views: 3496  Size: 24.8 KB  ID: 27615
Column would be made of aluminium, y bed 30mm thick, sides and Z bed 20mm, Z ballscrew support and supporting triangles 15mm. Rals for X would be Hiwin QHH20 or LGW20, for other two axis I can use SHS15R or LGW20 (that's what I have available).
Base structure looks flimsy compared to the rest of the machine, so I'm thinking of using 50mm thick granite slabs...