A single "master 3 way switch", whatever that is would have absolutely NO FUNCTION. It's 3-way operation only works when in series with another 3 way. From your description you want a standard toggle switch to energize two additional toggle switches. When you are downstairs turn either switch on or off, when you are upstairs turn the switch off to kill the lights and on to enable the downstairs switches to work. That is, unless you want to the 3 way to do something you did NOT describe in the original posting, in which case you might want TWO 3 way switches so you could activate or deactivate the individual switches from upstairs or downstairs.