He could be getting married to Ochaco Uraraka. They have a great friendship and there are many hints in the series that suggest a deeper connection between them. Their personalities complement each other well, with Deku's determination and Ochaco's cheerfulness.
No, it's not ethical. When a person is asleep, they are in a vulnerable state and cannot give proper consent. Any form of interaction without consent violates basic ethical and moral principles in a relationship.
Vandalism is also a form of trouble. Some high school guys might graffiti on school property out of boredom or to show off. This not only damages the school's appearance but also costs money to clean up. They usually don't realize the seriousness of their actions until they face the consequences.
One possible fanfiction could be that Deku discovers his new Black Whip quirk during a particularly intense battle. He's facing off against a powerful villain and in a moment of extreme stress, the quirk just emerges. It starts as a small tendril and then grows rapidly, helping him to bind the villain and turn the tide of the fight.
When a teen guy gets his first job, it's usually a mix of excitement and nervousness. My cousin got his first job at a local grocery store. He was excited to earn his own money but was really nervous on his first day. He was worried about making mistakes.
A teen guy's first haircut experience often depends on how he was raised. If his family has always been particular about haircuts, he might be used to it. But if it's his first independent haircut, he could be worried about making the wrong choice. My neighbor's son, for instance, was so hesitant that the barber had to give him lots of suggestions.
One common plotline could be Deku trying to hide his sickness from his friends at U.A. High so as not to worry them. He might keep pushing himself during training, which could lead to him collapsing eventually. Another could be his friends finding out about his illness and rallying around him to help him get better, like bringing him home - made soup and study notes so he doesn't fall behind in class.
Another storyline might involve Deku having to face some sort of villain threat right before the wedding. He has to balance protecting his loved ones and ensuring the wedding goes on as planned. Maybe a new villain emerges who wants to disrupt the harmony of the event. But with the help of his friends and his own heroic skills, Deku manages to defeat the villain and still have a wonderful wedding.