I don't know what it is supposed to smell like, I don't like it but am using it today in a recipe!
Nope, it's fine to use.
Probably not. Just stir well and it should be fine. Be mndful of the expiry, too.
I always taste it when in doubt. If it isn't good, you'll know instantly.
for your information, the liquid on top is some of the whey separating from the solids. whey and solids are the makeup of cream & milk. you can mix it back into the sour cream, use it in a bread recipe, etc. purchased sour cream will not go bad until it molds. it lasts weeks after the exp date. however, when in doubt don't use. don't ever taste foods you think have spoiled. the consequences of even a small exposure to some pathogens, you don't want to EVER experience.