My darkroom is in a spare bedroom. With two 6" fans blowing air out of the open window (via a light-trap) no smells reach the rest of the house at all. For my own comfort I use low odour fixer and stop bath in any case and most of the really smelly chemicals, such as some toners, can be used in daylight with the windows open. I have wood effect laminate on the floor - carpet is not a good idea for dust reasons. I would suggest removing or covering any existing carpet in the room where chemicals are in use, but that, plus effective air extraction and blackout over windows and doors is all that is really required.
So, basically, nope: running a darkroom inside the house, as long as you can vent air to the outside, will not cause any problems with smells or contamination.
You might want to look at this thread to see what others have done: (there was a url link here which no longer exists).
Cheers, Bob.