I'm a landlord and I do allow smoking in my two apartments. If it's any help, your landlord, should and I repeat *should* give you notice if he is coming to inspect the property for any reason. Usually it's a 24 hr notice.

Just air the place out once in a while, and I like Febreeze, it works well on fabric and curtains. Just don't be spraying the plants

As far as walls, depends what's on them. Some paint is washable, and some wallpaper is too. I think if you just smoke near a window, you'll be ok.