Shall i just buy a high quality gear outer and run it from shifter to derailleur? that will act as the 'stops' I need, right?

I am buying a XT rear mech on friday, and already have an XT shifter, with my new wheel too, and if I buy a rollamajig- surely that will help make things run nice. Should be able to get more than 3 gears. Even if the shifting still isnt perfect, its better than no improvement.