Sabina I grow in the basement and the smell reached a little up the stairway but seems to have stopped there. It probably depends on airflow patterns in your house, which to some extent will be determined by the degree of temperature inversion between upper and lower. If I had an attic that was useable I would probably put it there, though in my climate the heat would be a problem. Using a couple of good quality carbon filters would probably do it. I know many people swear by ozone generators, but I personally have no experience with them. When I re-design my rooms I am going to beef up my smell control.

Fungus gnats aren't really a probelem unless their population gets out of control. Seeing them indicates wet soil, so make sure you have good drainage and aren't watering when the soil is still wet. The larvae love wet soil. Get yourself a good quality soil moisture meter (cheap ones are very inaccurate) until you start to get an intuitive feel for when it's time to water. I use the pot-lift method, but it took a while before I got it down. Two simple treatments for gnats are blue or yellow sticky cards, which you can get through Amazon or any greenhouse/grow retailer. Just pin them near the soil horizon and those damn gnats fly right into them and become glued to their fate. Also layering sand or gravel on top of the soil makes it hard for the emerging adults to free themselves. Proper watering is the real key though.