i have a support thingy for the neck after it is already shaped...
at the absolute least you really need to have the taper cut and completely sanded to 220 and straight before you fret.but i would worry that the neck would move after shaping just enough to take my fretboard out of true...
this is the complete order i go in....laminate neck pieces together,plane and join completely square,attach fretboard,cut neck taper and headstock shape,cut neck profile,sand the taper perfectly straight,sand headstock to finished specs,drill tuner holes,shape neck to finished profile with rasp and sand it to 220,retrue my fretboard,recheck the slots to see if they are still the right depth,clean the slots and fret that bad boy...
fretting is dead last except for fitting the nut and installing the tuners..but i have reshaped necks after playing the guitar for a while...with strings still attached and tuned to pitch...