Daenerys Targaryen is a very likely candidate. Their connection through their Targaryen blood (Jon's true heritage) could be a strong basis for a marriage. They could join their forces, both having a claim to the Iron Throne, and rule Westeros together. Their marriage would also symbolize the unification of the North and the South, as well as the different Targaryen branches.
Yes, there are quite a few. You can start by looking on popular fanfiction websites like Archive of Our Own. Just search for 'Jon Snow married Val' and you'll find a variety of stories, each with their own take on how their relationship could develop into a marriage and what that would mean in the context of the 'Game of Thrones' universe.
One possible plot could be that Jon, after becoming King in the North, realizes that a marriage to Val would be a great way to secure peace with the wildlings. So he marries her, and they face many challenges together as they try to integrate the wildlings into the North's society.
Yes, there are. There are many fanfictions that explore the idea of Jon Snow getting married. Some might pair him with characters from the 'Game of Thrones' universe like Daenerys, Arya (in very different interpretations), or even new original characters created by the fanfiction authors. These stories often take different routes from the original plot and can be really exciting to read.
One common plot is the union for political reasons. Jon Snow might marry to strengthen the North or form an alliance against a common enemy. Another is a love - at - first - sight kind of plot where he meets a character and they fall in love and get married. Sometimes, it also involves him marrying someone from a different culture within the 'Game of Thrones' world and having to deal with the cultural differences in their relationship.
Jon Snow could potentially have allies like the Mormonts. They have always been loyal to the Starks. Maybe even some of the Dornish houses might side with him. They have their own reasons to oppose the current power structure in Westeros. And of course, his friends from the Night's Watch who left with him or believe in his cause could be his allies in this conquest. He might also gain the support of some of the maesters who see the value in his leadership for the future of Westeros.
The wildlings might be his allies. After all, Jon Snow has had interactions with them before. They are fierce fighters and could fight alongside him against a common enemy.
One aspect that fanfiction might focus on is how Val's wildling background interacts with Jon Snow's upbringing in the Night's Watch. Their cultural differences could lead to both conflict and a deeper understanding between them. Maybe in some fanfics, Val helps Jon Snow better understand the ways of the wildlings, which in turn gives him an edge in dealing with the threats beyond the Wall.
Sansa Stark might be involved as well. Given her relationship with Jon Snow as his sister (though later revealed otherwise), she could play a role in protecting or being involved with the baby. Maybe she helps raise the baby in a world where Jon Snow is constantly facing threats.
In this fanfiction, one of the key battles Jon Snow might participate in could be the Battle of the Whispering Wood. His skills as a fighter would be put to good use there, sneaking around and taking out enemies. Another could be a fictional battle near the Wall, where he defends against some new threat that has emerged during Robb's war.