It starts at a specific point in the manga, but I can't recall exactly without looking it up. You might want to check some manga forums or dedicated fan sites for the precise chapter.
There were many kinds of hand gestures for Gotto Gojo, including greeting, teleportation, and domain expansion. However, the specific description of the gesture was not found in the search results provided. Therefore, based on the information provided, I am unable to accurately answer how to do the gesture of Gojo Guru.
Nope, Marin and Gojo don't end up as a couple in the manga. The manga follows a different narrative path for their relationship, concentrating more on other aspects of the story and character growth.