When rendering beef fat for tallow, must the fat come from the cow's kidneys or heart area?
The source of the fat can make a difference in taste, texture, color, clarity, and fat composition.  (And that's not just the part of the cow, but also the breed of cow, how old it was, its diet, etc.)  The kidney fat, for example, is a particular area used from cows that produces a particular kind of desirable fat, but it's not necessary for making tallow in general.

As for odor, it's hard to say.  Rendering animal fats in general often tends to produce pretty smelly odors.  That's pretty normal.  You'll have to see whether the flavor is acceptable to you.  (I'd mainly be worried about odors from the fat before you started cooking it; in that case, it might be a sign the fat was old or even spoiled.  But odors during and after cooking can happen: a lot of smelly molecules are fat-soluble, so they may be released when it is cooked.)