1. How long does it typically take to go to go school? What’s the usual time range? 1 to 2 hours?
Typically, you need to be at school by 8:15 am.
If it's a public school in your designated district in a city in Japan, I would say from 1 to 30 minutes. An average would be a 10 minute walk.
If it's a public school in your designated district in a rural area, or if it's a private school, it can take anything from 1 minute to a couple of hours, and you might be using buses and trains. In rural areas, you are often allowed to commute using bicycles.
2. Can they bring skateboards to school? If they can, where do they put them?
In a typical Japanese junior high school in the 1990s, no, you were not allowed to bring skateboards. Skateboards weren't popular to begin with.
3. Who are the school staff? (Principal to teachers)
I don't understand the question. There is indeed a principal and many teachers.
4. What were the subjects back then? Are they different from the subjects today in Japan? And do every year (1st, 2nd, 3rd years) study the same subjects?
They were generally the same as today and throughout the 3 years. For decades, the 5 basic subjects have always been Japanese, math, science, social studies and English (as a foreign language). Then there would also be things like music, home economics and technology, physical education and morals. If you can read Japanese, Google 中学の時間割
5. How many class hours during Saturday for junior high school students?
In the '90s, Saturdays were already established as a day off at school.
6. Do sports and martial arts clubs have club rooms? Or do they just hang out in the fields and gyms?
It depends on the school. And mind you, very few junior high schools had/have "martial arts clubs".
7. What do you usually see in school hallways?
https://www.google.com/search?source=univ&tbm=isch&q=%E4%B8%AD%E5%AD%A...8. Do members in a sport (like soccer) that aren’t on the team need to practice? Are they as active?
Do you mean members in a sport club that weren't selected to play on the next tournament? Yes, they need to practice, and they are expected to be active. Mind you that club activities are optional, so if you don't want to be active, you are free to quit the club. Club activities are, of course, totally different from physical education class.
9. What are the school events that every school in Japan participate on?
Google "school events at a Japanese junior high school".
10. What do they usually talk about in Homeroom?
Whatever that needs to be discussed as a class on that day.
By the way, do you watch Japanese movies and TV shows staged at junior high schools? Most of them are accurate as far as your questions are concerned.
I hope it helps.