Well, having multiple bijuu sealed in him would skyrocket his power level. Each bijuu is a source of massive chakra. So, Naruto would have an almost limitless supply of chakra, making his jutsu much more powerful. He could also potentially access unique abilities that come from the combination of different bijuu powers.
Well, Naruto could face several consequences. Firstly, the sheer amount of chakra from all the bijuu might put a strain on his body. He could experience physical exhaustion or even harm to his internal organs. Psychologically, he might have to deal with the voices and personalities of all the bijuu in his head. This could be a real challenge for him, as some of the bijuu might have conflicting natures. Also, in terms of his relationships, some people might fear him or be jealous of his new power. This could lead to a strain in his friendships and alliances. And from a political perspective, other ninja villages might see him as a threat and try to either control or eliminate him.
New relationships could be very interesting. He could become like a big brother to the bijuu spirits. Naruto's kind nature would make him try to understand and protect them. The bijuu might start to see him not just as a host but as a true friend. They could share their stories and experiences with him, and in turn, Naruto could use their knowledge to grow as a ninja and a person. This would be a really unique bond compared to his relationship with just the Nine - Tails.
It would completely transform his power level. Consider that each bijuu has its own distinct set of skills and chakra reserves. Naruto would be like a living, breathing nuclear reactor of chakra. His ability to heal himself might be enhanced, as some bijuu are associated with life - force. He could also potentially communicate with all the bijuu spirits, getting their insights and battle strategies. This new - found power would not only make him stronger in direct combat but also give him an edge in terms of strategy and knowledge. He could become a sort of protector of the entire ninja world, with the combined might of all the bijuu at his disposal.
I'm not entirely sure if there is a specific fanfiction with exactly that premise. However, given the popularity of both Naruto and the concept of sealing powerful entities in Naruto's world, it's quite possible. Fanfiction writers love to experiment with combining different fictional elements, so it wouldn't be surprising if someone has written a story where Jenova is sealed in Naruto. You can try searching on popular fanfiction websites like Fanfiction.net or Archive of Our Own to find out for sure.
In many such fanfictions, it could be a variety of deities. It might be an ancient and powerful god from Naruto's world's mythology that the story's author has chosen to insert. For example, it could be a god of elements like a super - powerful fire god, which could give Naruto even more control over his existing fire - based jutsu and new, more extreme abilities related to fire.
With his enemies, it would be a whole different story. They might be more cautious about attacking Naruto. Some might even try to find a way to use the god sealed in him for their own purposes. And Naruto's relationship with the hidden villages could also change. They might see him as a potential threat or a very valuable asset.
Well, Naruto might become more mysterious. Since Gaster is an unknown and rather enigmatic entity, Naruto could start having strange thoughts or powers that he doesn't fully understand at first. He might seem more withdrawn as he tries to figure out what's going on inside him, and his normal cheerful and straightforward personality could be clouded by the presence of Gaster.
In many Naruto fanfictions, if Naruto has three bijuu, they could be the Nine - Tails (Kurama) which he already has in the original series, perhaps the Eight - Tails (Gyuki) as it has a connection with Naruto's world and Akatsuki's hunt for the bijuu. And another could be the Three - Tails (Isobu). However, it really depends on the specific plot and creative direction of the fanfiction.
His abilities would change in multiple ways. Firstly, his chakra control might be affected. Since Godzilla is a massive and powerful entity, it could disrupt Naruto's normal chakra flow. However, he could also learn to harness Godzilla's power within him. For example, he might be able to use Godzilla's raw strength to enhance his Sage Mode or even his Nine - Tails transformation. This could make him an even more formidable opponent. His speed could also be enhanced as Godzilla's power might give him a boost in his physical capabilities, allowing him to move faster and react quicker in battle.