Is there a limit to how much cosmetic surgery a person should have?

In terms of the amount of surgery that should be done at a single time, I limit my cases to 6 hours or less. This decreases the risk of problems with infection and blood clots, for example. See my earlier post about combined procedures here.
In terms of repeated surgeries or revision surgeries to a certain area, that's a separate question. Some patients sadly have to undergo revision surgery for rhinoplasty (nose job) at a rate of nearly 10-15%. This seems really high to me too! Revision surgery is also required in breast augmentation (breast implants) at about the same rate over a person's lifetime. Often this is to just go bigger, but it still requires additional surgery in some patients. The more you operate on an area, the more scarring that develops in an area. This can become harder and harder to work with and to shape. Imagine using a scalpel to mold concrete!
Facelifts are another surgery that is often "revised" but we usually call them "secondary" facelifts, because it's not so much that the facelift needs to be "corrected" but rather just "re-tightnened". A facelift turns back the clock about 15 years, so if you have one done at 60, you may want it redone at 75! That way you'll look like you're 60 again!