I, too, an a first time coach. If I didn't coach then they were not going to be able to have a JO U17 team. I read your response and would be interested in seeing some of your practice plans. We are only able to get a court 1 night a week for practices, so I don't want to mess up practices.
First of all, Welcome to Coaching!! On the plus side, you are already way ahead of the game due to your teacher's degree. John Wooden, one of the greatest basketball coaches who ever coached - anything - said that being a teacher was the best preparation for coaching. You already know how to help students learn, and that is exactly what a good coach does, helps players learn their game. If you need some help transferring your teaching skills to coaching, get "Science of Coaching Volleyball" by Carl McGown Phd. - Human Kinetics Publishing.
Rules: Lots of help here. Check with your AD and see if you are playing in a league or conference that already has accepted a specific set of rules. If not, next check with your area high schools to see what rule set your players will be moving up to when they leave your program, and use that set. If you aren't satisfied with that, call or email your local USAVolleyball regional office and get a copy of "USA Volleyball Domestic Competition Regulations" and go with those. If you have an area referee coodinator that your school uses, contact them to see if you can attend one or more of their training/refresher courses.
School athletic philosophy: What is it? How does your school expect you to treat winning and losing? Better check and make sure you and your AD are on the same track. Also, with 24 players, what are the expectations regarding playing time?
Speaking of which, since your team and schedule are already set, are there provisions for matches for your "first team" and another set for your "JV"? If not, could they be arranged? Or, might there be matches for the 7th grade and matches for the 8th? When my middle school program started getting 16-18 players a season, getting additional games was the only solution, unless you are willing/able to play completely different teams for each game of a match. (which experience tells me will satisfy no one)
Questions: Is your team boys, girls, or coed? Are you coming to a well established program or is it a year to year thing for the school? What is the current skill level of your players? - if you have had a chance to see. What about practice facilities? And, maybe most importantly, how will your "one period" practice session(s) work? For that one period a day, can you get all 24 players together, or are they split through-out the day. (I sure hope not!)
Lastly, what are you going to do at practice? Again, Carl McGown can help you with that. Or, if you need some suggestions or copies of practice schedules, I would be happy to send you copies of practice schedules I've used over the last 9-10 years.
Although this site has been "resting" for awhile, I feel sure that you will get a lot of additional help because there have been many, many great responces over that last few years.
Let us know how we can help, and how your program is going.