The tummy tuck scar should be well hidden by your underwear, so it would be below the top of the your underwear, going horizontally across. It may extend from hip to hip, or be a little shorter. The scar could be placed using the same incision as was used for a C-section. But the purpose of a tummy tuck is to get rid of any folds, so it wouldn't be located in one. The scar around your belly button would look like it's part of your belly button, so that shouldn't be visible either.
Belly button scars vary tremendously in their appearance with some being barely visible and others appearing red and thickened. This is quite difficult to predict.