The main differences are in their expressions and some minor details of personality. In the manga, Deku might seem a bit more intense, while in the anime, he's sometimes presented a bit softer.
Well, it's subjective. A waste of time for one person could be a great source of entertainment for someone else. It all comes down to individual tastes and what you're looking for in a comic.
Well, obviously Deku in two forms - the younger and the older version are the main characters. The younger Deku is the one who is still growing and learning, while the older Deku has more experience.
Another plot might involve the older Deku being from an alternate timeline. He shows the younger Deku different ways he could have developed his skills and relationships, which makes the younger Deku reevaluate his own path as a hero.
As of now, Deku is very much alive in the manga. The plot hasn't reached a point where he meets such a fate. Usually, main characters like Deku have significant story arcs and aren't easily killed off.
The title itself implies that it might be a waste. Maybe it has a convoluted plot that doesn't make sense in the context of the Peanuts world. For example, if it changes the personalities of the characters too much.
Naruto's outgoing and boisterous personality would make Deku more confident. He would probably be more upfront and less shy. Naruto's strong sense of justice would also intensify Deku's already existing desire to help others.
Bakugou could use his words. He might tell Deku that he believes in him. For example, he could say 'Deku, you may be a nerd but you're a strong nerd.' It's a backhanded compliment but it shows he has faith in Deku.
In the manga, Deku experiences various ups and downs. He not only becomes stronger physically but also matures emotionally as he takes on greater responsibilities. There are also many unexpected plot twists that shape his journey.