I've been asked to be a Head Room Mom for quite a few of my kid's classes. I have also assisted other room moms. Kids enjoy the parties because I like playing games (older kids think playing games and eating can be equally fun!) Teachers appreciate me because I don't abuse their classroom and parents like an organized party. Over the years, you figure out what works and what you will NEVER do again!
Yes, the idea of four "stations" are a great idea. Easy way to divide them up is name tags. Ask the school for 3 sheets of 30-up labels and use your computer to print the names on the labels (you'll have the names typed for future parties - make first name easy to see). The schools usually have die-cut machines so for Halloween, you can make four different name tag shapes...i.e. pumpkins, ghosts, apples and stars... that way, if you have one table that you really need all the kids to visit in a group, you can call, "Time for all the "pumpkins" to get their snacks and the "stars" can go to the craft table. Just remember to tape string - on die-cut because name tags must not be a choking hazard. Also, one extra set of labels can be used at the craft table to easily put names on craft and the third can be for any treat bag that will be going home.
Meetings are really a waste of time, especially in people's homes. If you really want to get to know people, just invite them for an afternoon snack and chat. Room mom meetings have always frustrated me..I quit having any more by the time my daughter was in first grade. People either don't show up or you spend two hours trying to figure out if you should play "hot potato" or duck, duck goose!"
Figure out what you want to do and delegate. Someone may grumble that you didn't have a meeting. Don't let it bother you. I usually am set on what will happen at the snack station but I listen to other's opinions on games and crafts. I have my back up games too. When they are older, the craft station is the one that goes away.
Re. treat bags: One parent can donate bags if you are having these. If you ask for bags....make sure they are flat-bottom-type paper lunch bags. If they are too expensive, individually, just buy red or blue lunch bag pack (of 50) at Target. Are you asking parents to donate treats (i.e. pencils, stickers candy, etc...) for a treat bag? Send the letter out...not too early, not too late. Delegate one of the parents to fill the treat bags in advance. Much easier to pass out a bag to each child than to sort stuff during a party. On your note that you would send home, ask parents to get the treats to the classroom, by (specific) date and give yourself the padding of one day for late-comers. Make sure you list the "allergy alert" on the parent note. Parents generally don't like treat bags, especially for Halloween; kids think they are great. I still do them and figure that, if a parent doesn't want to send in something, they won't.
Also, days before the party, depending on your school, the office will want a list of moms who will be attending party. It is also a nice idea to drop the teacher a note, days in advance, and let her know what you have planned in her classroom (i.e. 4 stations....here's what we'll do. Questions for you: So-and-so's mom will be picking up all treats for treat bags. Is there a date/time that I should tell her is convenient for you? Can we borrow your cd player? Do you have a table to set up snacks? Can I come in the day before to make sure all paper/food donations are in? ....
Also, those moms who are unable to attend, REALLY do want to be involved so make sure you call them so that they can help donate.
As far as food allergies, get the parents involved whose children have allergies. The "peanut" allergy mom may really want to be the one to create the snack or send in a snack for her own child. The "latex" allergy mom may inform you that there are other things that their child must avoid. These parents will really appreciate a call - they are the ones who hold their breath before every party in the hopes that their child doesn't have a reaction, especially Halloween.
Delegate, delegate, delegate and plan on being the "floater" mom. Should one station need you, you'll be able to give that area your attention.
Keep it simple. (Example) Station 1: Goulish (green Hawaiian) punch and halloween cookie...Station 2: Bat craft (make a bat using their white painted, hand prints on black foam or construction paper and use googly eyes...Station 3: Pass the eye-ball (hot potato)...Station 4: Some variation on ring toss, bozo buckets (or I have others!)
Have fun and good luck!