Is h-index important? Can h-index be used to classify yourself to know whether you are at a given academic rank? Of all the statistical factors that are used for judging publication record, the h-index seems to be the most commonly used

Wikipedia says


  Hirsch suggested (with large error bars) that, for physicists, a value for h of about
  12 might be typical for advancement to tenure (associate professor) at
  major research universities. A value of about 18 could mean a full
  professorship, 15–20 could mean a fellowship in the American Physical
  Society.


I am an organic chemistry with an h-index of 16. I assume physics should be similar to (organic) chemistry. I am now applying for a tenure-track position.
I mean to be overqualified for research funds, academic and scientific honors, etc. 

Questions


How important is the Hirsch index (h-index)?  
How much is the h-index really relied upon?
Can the h-index be used to categorize yourself? 
Can I really set a goal that by reaching h-index 20, I am at the level of fellows of my professional society?
Can the h-index be used to indicate whether I am ahead of my rivals?
Can we claim something by h-index or is it just a number?
What should be the h-index of assistant/associate/full professor in chemistry to be a leader of his own rank?
As with all bibliometrics, the h-index is indicative at best. There is no magic number that says "now give this person a promotion", but if you have an h-index twice that of your colleagues, it might suggest something interesting.

If you really want to use the h-index to see how you compare to other organic chemists, why not look at the h-index of your colleagues, collaborators, or of researchers at the department you're applying to? You will already have a sense of their relative position, you'll be familiar with their work, and it'll help you get a sense of what the h-index might mean in your specific field - as well as the amount it varies between individuals you'd think of as comparable.

(Make sure to calculate all h-indexes using the same citation data, though. You'll get confusing results if some use Web of Science data and some Google Scholar...)