One challenge is the lack of pure - blood Uzumaki. Since he is the last one he knows of, finding suitable mates with enough Uzumaki blood could be difficult. Also, the Uzumaki clan has a lot of enemies. Those enemies might try to stop Naruto from reviving the clan so they don't become a threat again.
Well, in some fanfictions, Naruto might start by finding suitable partners within the village. Since he is the last of his clan, he could look for women who are willing to carry on the Uzumaki bloodline. He may also use his influence as a hero to encourage others to support his clan - revival efforts, like getting the village to provide resources for the new Uzumaki generation.
One challenge could be getting the other ninja clans to accept his new clan. The existing clans have their own traditions and power structures, and they might see Naruto's new clan as a threat.
Well, he could start a family with Hinata and have lots of kids, passing on his Uzumaki bloodline. Then, he could encourage his friends who have some Uzumaki connection, like Karin, to also have families and pass on their Uzumaki genes. He could also set up a school or training center in the Uzumaki land, teaching the Uzumaki ways of life and ninjutsu, which would attract orphans or those who want to be part of the Uzumaki clan.
In harem fanfiction, Naruto could face the challenge of dealing with different cultural backgrounds of his partners. Since they come from various places, integrating their ideas and values into the new clan structure might be a headache. Moreover, resources are always an issue. Rebuilding a clan requires a lot of money, manpower, and materials. He has to figure out how to gather these resources while also maintaining his relationships in the harem. For example, some of his partners may have their own financial or family obligations that could either help or hinder his clan - rebuilding efforts.
One challenge would be getting other shinobi to join. Some might be loyal to their existing clans. Also, there could be political opposition in Konoha. The elders might not be too keen on a new clan being formed.
In fanfiction, Naruto may face challenges related to politics. Other villages may see the restoration of the Uzumaki clan as a threat to the balance of power. They could try to interfere in Naruto's efforts through various means such as spreading false rumors about the Uzumaki or even sending spies or assassins. Additionally, Naruto has his own duties as Hokage, so he would need to balance his time between running the village and restoring his clan.
In some fanfictions, Naruto might use a powerful jutsu he discovers or masters. For example, he could find a forbidden jutsu that has the power to bring the dead back to life. Maybe it's a jutsu that requires a great sacrifice on his part, like giving up some of his own chakra permanently.
In this fanfiction, Naruto could reject his clan because of the dark secrets or past actions of the clan. He is a character who values justice and friendship. If the clan has a history of wrongdoings that he discovers, he may not want to be associated with it. Also, Naruto has his own dreams and goals that might not fit within the framework of the clan. He has always been a bit of a rebel, and rejecting the clan could be his way of standing up for what he believes in.
One possible reason could be to seek greater power and training opportunities elsewhere. Maybe he feels restricted within his clan in terms of the type of jutsu he can learn or the level of training he can receive. So, he decides to leave to explore different ninja arts and grow stronger on his own terms.
In some fanfictions, Naruto might restore his clan by using a powerful jutsu to bring back the dead members. For example, a fictional super - level resurrection jutsu could be discovered. However, this would likely have many consequences and moral implications within the Naruto universe.