Hi, im pretty new here as well, however I was just looking at the stepper motor size, and they strike me as being pretty over - spec. My machine works with aluminium reasonably happily and accurately, and just about with mild steel, and it uses 1.89 Nm steppers. In terms of wood (I've only cut softwood though) and plastic, both are far easier - my 2.2kw spindle will happily do 1000mm/min, 10mm endmill, 5mm DOC slotting, which is more than fast enough for me. so unless you're trying to work with some really tough woods and plastics really fast, or you're desperate for lightning rapids, I doubt you need that amount of power. Of course, more power usually doesn't hurt, so I'd get some 2-3Nm steppers and put them on your old machine, then transplant the 8.5 Nm ones to your new machine (although save one for your rotary axis). In terms of rails, I'd say that 25mm Hiwins also sound pretty overspec. even dedicated metalworking machines often seem to use only 20mms, and unless you're wanting accuracies above around 0.05mm, I doubt you'll really need the properties of profiled rail at all, but will still need to deal with the hassle of mounting them on a flat enough surface that they don't seize. Personally, I found that SBR 16 round rails performed "well enough", certainly for wood cutting. Instead of spending too big on the hardware, I'd recommend focusing on the design - making sure the gantry sides are as triangulated as possible and maybe using a big piece of aluminium box-section extrusion to try and get the gantry as resistant to torsional and flexural forces as possible. also, the Z axis will have the most difficult loads to deal with - try to get the linear bearings far apart for extra stiffness.