I teach all sorts of circuit, bootcamp, obstacle course type training, tabata, etc… you can do 4 stations max… that’s manageable. Break it up into Cardio, Abs, Upper and Lower body and keep the exercises simple at first then build up as you continue to teach. This gives your clients a chance to get to know your style, your verbiage, and the exercises. Before long you’ll have some veterans in the class helping the few new people that show up late or later in the year.
I started teaching a similar class with about 15 people and started with 30 seconds 15 second break and then 60 seconds on the same station. I gave quick review of what we would be doing at each station. While they were there for 30 seconds I watched them carefully and made some minor corrections as needed. During the 15 second recovery I went back over those corrections, i.e. — squat back, weight over heels, bicep curl keep arms still, move only elbow joint, abs lift shoulders towards ceiling, etc… then told them to give it their best shot over the next minute. They can always stop and walk it out or take a break or tone it down if they are super tired and not able to do the whole minute. Eventually I switched the numbers and did 1 minute then 30 seconds…etc…
One minute of any exercise is really not that difficult even for the novice as long as you let them all know at the beginning of the class… if the exercise asks for a jump squat, just do the squat… listen to your body and your perceived exertion, drink water as needed and stop and walk it out when you need to.
Over time you get to know your clients and you know their fitness level, their weakness and strengths and then you can work with those individuals in the minute or two at the end of class encouraging proper form to avoid injury, etc.
Hope this helps.