The factthet people go to kill hrmselves over there does not mean EVERYONE kills themselves when thry go to the forest. It was (as even stated in the movie) a popular tourist attraction, so as long as people were careful not to get lost, things should be OK, and if anyone will want to commit suicide, they will do it anyway, forest or not.
2- students were scared as they were certain their teacher was dead, and they thought she turned up, and they could not rationalise it up until they wwere told it was a twin. That I thought was quite clear, not sure where your confusion comes from.
In the beginning there was nothing, and it exploded.

the student was just a dumb teenager. ghosts probably cannot leave the forest, she just got super scared

Oh dang, looks like the forest is closed. I guess I'll just continue suffering in my useless existence.

whether you destroyed it or managed to put a huge guarded fence around it, it woulnt prevent suicides, people would just find another suitable spot to do it in or find a way in.

Hey, Japanese guy here.
You might wanna check the VICE doco if you want more info on this topic.
As for 2) It's just a cliche horror ending. The ending would have been 10000 times better if Michi just leaves after seeing ghost Sarah but I guess the director/producer/writer's vision sucked. Plus, ghosts in any culture cannot move around that much.

1. It's like Golden Gate Bridge. You can't just get rid of a place like that. We're talking about an entire forest at the base of Mt. Fuji. There are many "popular" suicide spots in other countries and they usually have signs with lifeline phone numbers.

This message has been deleted.

I read that the movie wasn't entirely filmed in
Ja
p
an
, so maybe it's different in real life. The movie makes it look like everybody just accepts the suicides.

Being 35km you could enter from anywhere. Wouldn't need an entrance
Next question, I've never heard of spirits leaving, just haunting the forest.