My advice:
Get out of chaperoning duties and go as a "supportive parent"!
My friends and I did on 2 seperate trips and had the time of our lives! We were still there for "the kids" but were able to be more flexible with our time. Since that doesn't seem to be an option for you I would recommend:
1) Talk to friends (or band kids) who HAVE been to Disney World; get their advice, recommendations, mistakes they made, what "worked" for them and ask if you can see their photos.
2) Purchase or check from your library any/all information books you can find...or afford to buy...and read them!
3) Read as many threads on Disboards as possible. While this is time consuming it is SO worth the effort.
4) Research you resort. If you're staying at a Disney Resort find your resort on the Resorts & Videos threads. Valuable information there from previous guests; if there are no picture threads, ask previous guests to post their photos with any advice they may have.
5) Get the proposed schedule of the ENTIRE trip from your band director as soon as he/she has it available.
6) Will the band be participating in concert or marching form? Oldest DD's group marched in the evening parade; youngest in the afternoon one. They run from Frontierland (by Splash Mountain) to Main Street, exiting to the right of the Fire Station...or visa versa. Walk the route (in your spare time
) to determine your ideal spot for picture taking. Our favorite spots were Main Street (around Plaza Ice Cream Parlor...for "front on photos"...especially nice with the Castle in the background) and row by row closeups; front of the Castle (facing Castle to the right); Liberty Square...on the "curve" in front of the Riverboat toward Frontierland or at the beginning (or end) of the parade...as close as possible to Splash Mountain. Station yourself on one side of the street; have another chaperone on the other side for photos. Claim your spot AT LEAST an hour before parade time.
7) Allow 20-30 extra minutes to "meet a deadline"
. In other words, if your entire group is to meet at, say the Epcot entrance at Noon...start walking toward that entrance at least by 11:30 (in Epcot's case...if you're in WS you need to add another 15 minutes!).
8) Our kids were allowed to "be on their own" but we stationed chaperones at a popular spot in a park so they would be available to the students if needed. Of course, that was 12-15 years ago ... no cell phones. In "this day" I'd make a list of students cell phone numbers and a seperate list of chaperone numbers making sure EVERY student had that list.
9) Recommend to the kids (and adults as well) to take twice as much spending money as you think you'll need.
10) Bring ponchos...9 out of 10 chance it WILL rain.
11) SUNSCREEN...I won't go into the whole sad story but my now son-in-law and a group of his friends have first hand information on how painful it is to wear a scratchy, stiff band uniform over severe sunburn!
12) Play the "What If" game...and play it again!
We had a "free day" at the MK before marching in the evening parade; one of our charter buses had engine trouble on the way to the park ... WITH THE INSTRUMENTS!
We can laugh about it now but it WAS NOT funny at the time!
13) Review/familiarze yourself with the food service establishments and their menus if you'll be responsible for purchasing your own meals. Ideally, a list for the kids of restaurants/quick service facilities, a brief menu and prices would be most helpful.
14) Take pictures; and more pictures and MORE pictures! You can always delete the bad ones but you can NOT have "to many" of the good ones!
If at all possible, arrange for a group photo in one of the parks, taken by either a Disney photographer or a parent. You can, upon return, make that photo available to any of the band students desiring a copy.
I'm sure I'll think of more but these should get you started. DD and her husband took DGD's soccer team (10-11-12 year old girls) to DW in July for the International Soccer Tournament; a first time trip for many of the girls as well as their first experience flying. I'll ask her if she has any suggestions for you. It may be 6 months away but time is short! Being a first time visitor can be overwhelming...spend every spare minute in these next 6 months educating yourself on the "wonders of DW". You are about to experience a "trip of lifetime"; be prepared and the fun will follow!
PS I AM more than a little jealous!
or a cup of ice coffee from HS Writer's Stop) and just sit for 15 minutes and people watch. Watching "your kids" perform at WDW is a "never to be forgotten moment" you'll cherish always! Good luck; have fun and let us know how things went...complete with pictures! 
