there is an abundance of suitable material available for starting from the ground up. I would suggest as a tune, the air force hymn as it is often requested and rarely performed. Here in Vancouver for the Battle of Britain remembrance, the Air cadet band present, although skilled could not perform any of the tunes expected of them.
Focus on 6 tunes of your choice and stick with them until your cadets are ready to puke. Having had this very experience on a number of occasions, I can honestly state that people take you much more seriously if you play tunes that each member is confident with. A much better sound is created when everyone knows their place within the music.
Until your core group is settled, do not change the Set list unless your cadets tell you otherwise.
If you are starting from scratch, with novice or unskilled players, be sure to attempt to recruit help from wherever possible. Personally speaking, as long as the individual is not responsible for any costs (ie: Security check) you should be able to get a few people who can help out greatly. I have dealt only with pipe bands, so my advice may be a little off the mark but be sure to keep the kids engaged and DO NOT neglect any sections overly. If you have experienced musicians to start with, use them as much as humanly possible.
Good luck,