Re: Visiting Karachi
You can go for a pre-booking in any Hotel (which you can search over the internet, I would have recommended you some names but I dont know which City you will be landing in first). You can find a Radio Cab at airport which will take you to your place. and then you can enjoy your holidays 
Tips/ advise: Dont let anyone know you are visiting here for the very first time or you have no relative here!!
Always Bargain when buying something or taking any services. They always tell you the extra cost 
Have a lot of patience for facing the very hot weather/ power failures/ bad internet connections!!
Bring Summer clothes along!!
Aur yaad aaya to batadungi 