Ok I will spend some time converting it all to 80mm box, what wall thickness would you recommend?

Those rails are only for an idea of where everything will go, in the end I will use Hi-Win rails all round as I have read a lot about there flexibility in use and strength, I just couldn't find a model of then in Sketchup so put the SBR's in just for reference. My main priority is getting the frame completed as I would like to do the build in phases.

If I extend the uprights and use the plate method to true it all, will five uprights be enough/too many? Or should I leave that as is?

Also, should I leave the bed in 100mm box as surely that will need as much strength as possible?

Thanks in advance guys appreciate the time taken to help!