Designing a Halloween Escape room for my elementary school

Hi! I am new to the sub and I am very glad it exists! I am looking for some organization help in planning 2 escape rooms for the upcoming Halloween event at my kid's elementary school. I have attended quite a few commercial escape rooms myself and planned scavenger hunt for my young kids at home, but have never planned an escape room this scale.

The event will be 3 hours, and this will be for Grades 2-8 (age range from 7-13). So I am thinking I'll probably need 2 rooms with different level of difficulties for the puzzles. Location will be in a multipurpose room that I can reconfigure, it is also attached to the school's small library. Another will likely be in a classroom. 15 mins sessions with 5 mins reset so that I can run through as many students as I can.

What I have done: I have looked through various posts here and /escaperooms and Constructedadventures website blog & tool box so I have some ideas of individual puzzles (UV light message, hidden key in slime, jigsaw puzzle, Popsicle stick puzzle, etc). I am also borrowing the "rescue the mascot" theme that I found in an older (post).

What I need help with:

- a high level approach - should I do mostly linear structure? how many puzzles should I plan for?

- Is group of 6-8 kids per session reasonable? Or less for the easy room and more for the harder room?

- What are the things I should keep in mind for a short session like this? We will have 5 mins of reset so I'l make sure whatever puzzle/gambit I use can be reset easily. As much as I would love to do a potion mix, I won't be due to the short reset time

If you have done something similar in a school setting, I would love to hear what worked and what not. Thank you all!