I know that em-dashes can be used to surround parenthetical statements, but other than doing it the usual way—surrounding extra content in two em-dashes—it is allowed to surround them with a total of three, two at both ends, and one in the middle?
For example, I know that instead of using an em-dash in the middle, you can use a comma instead. However, would the following example be correct (just something I thought of off the top of my head, so some phrasing may be a bit incongruous):
Although your grades do not represent everything and you can indeed find a successful career without even going to post-secondary education—quite an expensive choice, by the way—not a common path to take—I recommend you study hard and aim to enter a post-secondary institution if possible.
Both of the phrases surrounded by em-dashes can be excluded, but would the consecutive use of em-dashes like that be correct, and/or advised?