I'm not sure which novel you're referring to because you didn't provide any context or relevant hints. If you can provide more information, I will try my best to answer your questions.
The house might hold the truth about Naruto's birth. There could be records or something that reveals more about the circumstances of his birth, like why he was chosen to be the Jinchuriki of the Nine - Tails. This would be a huge revelation for Naruto.
It depends on a lot of factors like the construction materials, design, and local building codes. But generally, a well-built 2-story house can hold a significant amount of weight.
You shouldn't hold up manga because it disrupts the normal distribution process. Publishers have schedules to keep, and holding them up messes with that. Also, it could potentially lead to legal issues.
In some manga, a boy and girl friendship can hold up. It often depends on how the authors handle the relationship, the common interests or goals of the characters, and the way they support each other through various situations.
It depends on a lot of factors like the construction materials and the design of the house. But typically, a well-built old house's second story can hold a considerable amount of weight.