The model at the moment is just a rough, I will join up the supports it was just pain in the butt trying to rotate things in to odd angles in sketchup. :)
I was going to epoxy to avoid any welding distortions, the rear struts I will weld onto plates and then epoxy all the rear strut plates on to the beams in one go.
My maths still isn't good enough to confidently sit down and work it out, so thanks for that!
I'm almost positive I won't upgrade to guides, if I upgrade this machine it will be to extend the x-axis to cater for 8x4 wood sheets and I can't really see anything I'll be doing at size needing the accuracy of guides.
If resonance does become an issue I always have the option of filling the beams with vermicrete or something similar, a poster over on practicalmachinist reckons truck driveshafts just use thick cardboard tubes inside to dampen vibrations.
The epoxy path is starting to get expensive, £120 quid just for a flatish surface which would mean I would have to ditch the shiny leadshine drives. I think I'm going to have to see if I can find some where local with a decent sized surface table and use the cheap stuff & clingfilm method...