depends on strain, but generally weed stinks when it flowers. If you dont use any odor control method then your entire room, or even your entire house will stink of MJ.
What kind of filter a carbon filter or what. And if you do mean a carbon filter, where could i purchase one for cheap.
The smell usually will start becoming potent around week 3 or 4 of flowering. My advice, get an ozium dispenser for outside of your room, and it sounds a little ridiculous, but having an air-conditioner in your setup will actually filter the smell pretty well (and keep the temperature at a firm 72 degrees).