I'm in exactly the same situation. The question is how much time would you devote to fitness in a beginner class and what exercises would you do? Also, would you discourage advanced students who want to do strength training on their own, or let them make up their own minds about that?
BTW our beginner class just moved into a new room at the facility I use, and it's got mirrors on all the walls... doesn't exactly help to reduce the "vanity factor!"
I usually give them about 20 mins at the end of the class , I start them off with some chain punching in the air for about a minute , then 10 reps on each leg of any kick of your choosing , then straight down for either push ups , burpees with a push up and jump , or body weight squats.
I give them about 10 to 20 reps of these exercises depending on their fitness.
After they finish the chosen body weight exercise get them to stand up and jog on the spot for a couple of seconds to catch their breath and then make them measure out their stance and start chain punching again , and the cycle starts again.
The couple of seconds jog on the spot and the chain punching in the air serve as an active rest period before the next round of kicks and body weight exercises .
Towards the end start making them chain punch whilst in a low horse stance for a bit of extra pain.
Then finish with stomach crunches and a few stretches.
If you have equipment like focus mitts and kick shields you can divide the class up evenly into lines facing each other and do power training.
One side holds the pads and the other side does 10 reps on each arm or leg of a technique chosen by you.
You set the pace by calling out the count , 10 reps for each side of the body , then the pads get handed over and its the other teams turn.
Keep the count at a fast enough pace so that they only have time to reset their stance before executing the next strike or kick.
Intersperse these single strikes and kicks with a minute of chain punching at moderate speed on the kick shield and then on a signal from you they go flat out for 30 seconds trying to drive their partner across the room with their punching power and stance.
When they get a bit more advanced you can also just let them do light hand sparring from the guard , by that I mean facing each other in Wing Guard and they have to step in and use their techniques to penetrate each others defences and strike through (no legs just hands).
Make sure they rotate frequently and get a chance to spar with as many different people as possible.
I do moderate strength training as well so I can't really tell them to not weight train , I just tell them not to go overboard or they might get sore from the last weights session and can't do Chi Sau properly.
Its great you have a place to train at with mirrors , they can be a bit of a distraction , but one thing about them is that they don't lie , they can show up a lot errors that you didn't even realise you were making.
I'm still teaching at parks , high schools and students houses where ever theres a bit of space and shade basically.
But I suppose its not the venue that your teaching at that counts , its the quality of the people you are teaching , and my guys as few as they are train hard and don't mind taking the odd hit either.
You can't ask for much more than that.