Hello Gaby, welcome to UsingEnglish!
Yes, I think they can all be construed as gerunds. You can take the INGs as objects of the prepositions "by" and "after" in numbers 1 and 2; similarly, the first ING in #3; and the second one in #3 as the object of "started".
I have seen long discussions about whether certain kinds of ING are participles or gerunds, though; so other members may disagree!
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