Forget the printer being desktop, use a ballscrew directly under the table like a knee mill and spin the nut, use a large single Hiwin rail and block for the table guide. The printer has to have an enclosed metal chassis for rigidity. Look at aircraft spars or carbon cycle tube for the gantry design, you are looking for light very low flex. The more weight in the XY, the more inertia you have to deal with. Servos are a step too far on cost, but if cheap hybrid ones become available... The nozzle is lightly loaded, but direct drive for the filament is a must, a weight penalty on the gantry. Bowden drives have too much hysteresis for accurate metering of extrusion. The 3D printer has to be looked at as a high speed motion device, not a cnc milling machine, but still requires high prescision. My downfall is not having access to CNC machining for parts. Printed parts are OK for testing but not the finished item. My build volume aim, 300mm x 300mm, with a 400mm Z. That would make the printer about a metre tall, so mostly storage in the base.