All good feedback! Been thinking alot and got a good contact for z-plate milling, so thats coming along ;)

New thinking and new problems!
Im going with welded steel frame, around 60x60x3mm for x rails and legs.
Now for the question.
Can I use something like 40x40x2 or even 30mm for bracing?
What measure should I use for the bed? The total size should be 1500x1500mm (maybe smaller in y, total 1000mm but I would love the posibilities of 1200 workable area)
Im thinking of making a frame and then crosssections along y axis only about every 300mm? Maybe with 40x40x2mm steel?
And then one under all of then in the x axis in the middle for sag support?

Would love to show a cad drawing here but my computer died and Im restricted to using a phone at the moment.

Regards
Madman