I have used unity for about 2 days.  My engineering assignment for my class is to create a lock down drill for out school.  I have the model of the school, another group is working on making characters of some random classmates, and another is working on sounds.  I need to improve the school model a bit but that shouldn't be all that hard.  

There needs to be a simple menu with some basic options.  like pick if there is an inside or outside intruder, what room to spawn in, npcs students that respond to the threat, a roaming intruder npc (no guns or anything bad because it is in a school) and then teacher npcs that will get up lock the door etc...

Was wondering if any of you guys could point me in the right direction with where to start this project.  I am guessing this will be a rather large project any help would be great.  I have done some Arduino coding which is similar to C, and HTML and CSS (guessing not much help because that's website coding.)

Any help would be amazing.  Thank you in advanced for any advice, or examples.  I have quite a large time frame for this project so no rush.