The biggest issue you will snag into what the old T&K were run is the power source it is very common to find the power source at the luminarie junction box ( I know there are few case no junction boxes at all ) and you mention three ways this will get more trickier to deal with it due some of old T&K three way still wired in Carter format ( it been discussed in few thread in the fourm but I will post the diagram so you will get the idea ) and for myself I will not try to attempt to save the exsting circuit due the key issue is ground conductor and with romex cable most older one do not have ground conductor in there so I will not touch them useally they go out of window.
If you have ballon frame house it will be little easier to do this if the wall is not really insulated well you can fish them thru the wall cavity without much effort.
Expect some holes show up a good electrician will keep the holes to bare minuim depending if you do not have hortzonal fire block you are ok with it ( on the wall ) but expect that going to be happend.
Otherwise inside wall is next best choice if you only deal with one floor you will be ok.
But that pretty much up to the electrician call what they think the best route to run the new conductor and see what they think about it.
I will post the cariter three way switch set up look like in case you still have T&K in the switch box.
Expect that if you do have T&K at the switch box this will be a one way you can be prepared for it.