Deku can use 100 percent in the manga, but it's usually a last resort or when he's facing an extremely powerful adversary. This power boost often has significant consequences for his body and abilities afterward.
I'm not sure of the precise percentage. Different people might have different estimates. It's best to keep up with the manga's ongoing chapters and see for yourself how far Deku's story has progressed.
It depends. Sometimes Deku can manage to use 100 percent without getting hurt if he has mastered certain techniques or has received special training. But usually, it comes with a risk of injury.
The percentage of Deku's power usage changes based on a lot of factors. Like the nature of the enemy, his training progress, and the urgency of the situation. So, it's hard to give a fixed percentage.
I'm not sure of the exact significance of '23 percent' in it. It could be an arbitrary number the author chose to mark a certain part of the fanfiction.
It's hard to say for sure. Deku has grown a lot, but All For One is a powerful villain. It depends on various factors like their current abilities and the circumstances of the battle.