Looks like a nice all rounder Jim.

I'm sure it'll be up to a decent level of performance for wood and would do alu too.

I might put another one or two uprights in supporting the steel section where the x rails are mounted. There's only 3 and that looks like quite a tall span you have there.

With 20mm profile rails on the Z and an adjustable bed there's no need for such wide bearing spacing. You could bring them closer so the top one has its bottom edge in line with the Y blocks.