Hi John
I would suggest, carry on with your Kurta and go all the areas (exceprt sub-urb or no go areas) Karachi is one of the most lively city in Pakistan, beautiful beeches, metropolitan lifestyle, best foods and so on,, how ever you must know the right people who can introduce you right places, as far as your wife look , there are many with similar Kazak look in northern part of Pakistan, if she wear local dress , hardly anyone will mark it. If she can speak English ,even would be no problem in mixing people. Good luck and be excited,, Dont be worry
Cheers