This depends a great deal on the individual patient and the type of skin but unless you gain weight the results are very long lasting. Almost all surgery can be repeated. Still for most patients this is not needed. This is usually not a problem. Secondary liposuction can sometimes help if you gain a small amount of weight.
Cosmetic surgery is a very personal matter.
Only you can decide who should and should not know you have had surgery. I recommend that you talk about surgery with at least one other person you know well. Your spouse or a good friend are obvious examples. You could also discuss surgery with a therapist or your family doctor. Unfortunately, even today many professional people are not well informed about cosmetic surgery.