Too much to talk about, but not sure what to say?

My old Best friend(from kindergarden until 4th grade) moved away 5 years ago. I have had no contact with her what-so-ever. She is a senior this year, and for her open house she is coming home. I only get a little bit of time to see her. How do I talk to her, like what are the most important things to talk about. Should we remember the past and all the great times, should we talk about what happened in those 5 years apart, should we talk about the future, where she plans to go to college and what she wants to do, or where she will live. stuff like that. I'm soo excited, but also worried that since she hasnt seen anyone else from here for the same amount of time, she won't spend much time with me. She was my BEST FRIEND, Like a sister to me, and when she wrote she gave me her cell number so I can text her, but what do we talk about when she is here for only a few days(1 or 2). and How do I say goodbye to her again. It was soo hard the first time, but maybe because we were so young?(she is 4 years older than me, just incase you are wondering about the ages, im 15, she is almost 19)