One big challenge could be gaining the respect of the older and more traditional ninja in the village. They might be skeptical of his youth and inexperience. Another could be dealing with political intrigue within the village and from other villages. Since he's young, they might think they can manipulate him.
He might become more serious. He realizes the weight of his responsibilities, so he's not as carefree as before. But he still tries to keep his positive and determined attitude.
One of the most dangerous challenges is the lack of proper guidance. Without a teacher, he could easily misuse chakra and harm himself. For instance, when he first tries to perform more complex jutsus, he might not know the limits of his body and chakra reserve.
In many fanfictions, one challenge is dealing with internal political unrest. There are often clans in Konoha who may not fully support Naruto's new ideas as Hokage. Another challenge could be external threats from other villages that see Naruto's new leadership as a potential threat to their own power.
One challenge could be readjusting to the village life. After intense training in a different environment, the daily routines and social norms of Konoha might seem strange. Also, he may face jealousy from some of his peers who haven't advanced as much in their skills during his absence. Another challenge could be dealing with the new threats that Konoha might be facing, and having to prove himself all over again to the village elders that his new skills are useful for the village's protection.
One challenge could be facing powerful new enemies. In fanfiction, authors often create unique and formidable foes for Naruto. These enemies might have strange powers or abilities that Naruto has never encountered before, forcing him to quickly adapt his fighting style. Another challenge could be the moral dilemmas. He might have to make tough decisions in the chaos of war, like whether to sacrifice a few to save many.
Well, in some fanfictions, Naruto leaving Konoha for training means he has to face new enemies outside the village. These enemies might be more powerful or have different fighting styles that he's not used to. Also, he has to manage his resources on his own. Without the support of Konoha, getting food, water, and training equipment becomes a problem.
In this fanfiction, Naruto might become a Jounin at a young age due to his extraordinary growth. Maybe he has a special training regime with a powerful mentor. His quick rise could also be because of a new and powerful jutsu he discovers. This would make the village elders recognize his strength and promote him early.
One challenge could be leadership. As a Jounin, he'd have to lead teams. Naruto has always been more of a lone wolf in some ways, so coordinating and guiding others might be tough. Also, there would be more complex missions. He's used to straightforward 'beat the bad guy' type of missions, but now he has to deal with politics and long - term strategic goals.
He could implement a policy of more open communication between the different ninja clans. This would strengthen the unity within the village. By having regular meetings and exchanges, misunderstandings can be reduced.
Well, he might implement a policy of more open communication between the different ninja clans. Since Naruto has friends from various clans, he would want to break down any barriers. For example, he could start regular meetings where clan leaders can discuss issues freely, promoting unity in the village.