I need plot help; story 1 of 3 (title suggestions welcome)

The admins in charge of this board are welcome to either move this thread to a better place for it or comment and I'll do it.
I have this idea for a novella (or even a novel) in which a college freshman donates a bunch of her old books to the school library during a book drive. The problem is, she put her phone number into several of her books (such as ones she took on vacation or somewhere they could easily get lost) and forgot about that until she left. Later that day, she gets a phone call from a recipient from one of the books. He was calling to ask what she thought about the one he'd picked up, because it was required reading for his English class. They hit it off immediately and their friendship grows as time goes on. This is where I'm stuck. I'll put this into a manageable list.
1. I can't decide what sort of time frame I want. The semester? The school year? Even longer?
2. Should there be any sort of serious obstacle--such as her being terminally ill? What about a retelling of the story of the kid who was going to commit suicide but an act of kindness from a stranger saved his life? I really like that idea, but you guys can throw more ideas at me.
3. There has to be some sort of conflict. Do the characters have friends or family who are trying to get them together/pull them apart? Does one of them have some sort of secret they have to keep?
4. How should it end? Cliche, like falling in love and living happily ever after? Unexpectedly, like one of them falling in love with someone else and having the other's blessing? Tragically, like a death or long separation?

Title:  One Life to Live
On # 1  Try for a semester but have goals for the future.
On #  2  A serious obstacle?  I'm no help there, I don't like to write about traumatic experiences for conflict.
On #3 What about a possessive dad that is determine that his daughter is to finish college and is constantly talking down to her about any close friend she might acquire because he is afraid it will distract her.  He wasn't able to finish college and he is obsessed with trying to control her every decision.  Could be good for some good dialogue.
# On #4  What about the both guy and girl joining the military but they keep in touch. He joins because he feels it is his duty and she joins to live her life as she pleases.  Their romance deepens through letters.
Good Luck, Christine

It depends first of all on your purpose for writing and the overall theme you want to adopt.

I think after you've got those two down, it's easier to deal with questions like the ones you asked.