Okay, I'm not sure if my answers will help you or not, but here it is:
1) Since the only thing I really have figured out right now are the opening scenes, I'd like to start with what I know and then completely wing it. In that case, I'd like to start with Allie and Jack wandering around the fair, where they run into Dom, Chase, Kendyl, and the rest of their group. At this time, Dom makes her presence known to Jack and Allie begins to wonder who she is. In the meantime, Finn is hanging out with Shawn, telling him about how a very pretty girl (who is actually Allie) has just moved next door, and that he is excited to meet her. Shawn pays no attention to this and is in his own world complaining about how Jack has spent no time with him, and that he misses his friend. Shawn sends Jack a text, which Jack ignores since he is with Allie. While this is happening, Blair has just learned of a few parties in their hometown and desperately wants to take Allie and Jack to one, even though she knows that Jack will not be interested in it. She decides to send Allie a text about it, and Allie decides that she will later ask Jack if he would want to go. And lastly, while this is happening, Paxton and Asia are discussing the fact that he is taking her to meet his family (Allie, Jack, etc.) and are contemplating telling them about her job, addiction, and lifestyle.
I want to play this whole section out, and then after that, it will be totally free fall, the whole plot could change.
2) I'm not being picky, whatever best suits the situation or your writing style is totally fine. If you want to go far into detail, please be my guest! If not, that is completely fine. Whatever works for you.
I hope this answered your questions? If not I'll be happy to try again, haha (=