Viper,
If I am understanding you correctly, on the adjustability, I think if you use a master template to route all of the pieces then the only adjustment that should be necessary would be to the bearings on the gantry & the z carriage. Everything else should be very consistant. You may have to shim in a few areas but I don't think you would if you assembled the machine carefully, paying close attention to the alignment of the pieces and to the squareness of the parts.
If the design is well thought out it should go together almost like lego blocks. We should design this to have half lap joints in the torsion boxes so it goes together like a drawer divider. this will greatly eliminate the build errors.
Hope this sheds some light on the idea that I have
Jimmy Southern