Oxygen and Hydrogen are combustible gases, water a mixture of both is a fire extinguisher How?
If it doesn't catch fire after a few hours of operation while you're awake, it probably won't catch fire while you're asleep, either. Give it a good inspection, paying particular attention to the power cord: look for cracks or damage to the cord, especially near the plug. Forget about using it overnight if you have a pet that might knock it over. Make sure it's in a clear area, away from anything that might catch fire, like drapes or a tablecloth.
A few things I have learnt over the years. You just bought the New Heater, I would trust the thermostat controls. Set it to the temperature you want and leave it in a safe place. Keep in mind. Long extension cords and heaters are bad. You need to keep you water pipes from freezing. Use the summer fans to de-stratify the warmer air at the ceiling. To stop pipes from freezing just open the taps ever so little for a running drip, moving water has a hard time to freeze. Lastly aluminium house wiring and heaters are bad. Be safe and take care, warmer days are coming. Smile, it is colder here, crunch crunch
Electric space heaters are very safe unless something such as a towels or paper falls on top of them. They are even safer than gas space heaters because they don't have a flame that can travel from them to a flammable object. They have to heat the object to combustible temperatures first.
I'd say, figure out how many you can COMFORTABLY do that night. Remember to keep time for yourself to get ready and look beautiful. If it's going to stress you out too much, take less people. Be generous since it's obviously something you love to do, but don't give at the expense of having a good time at prom yourself. Keep some styles on hand for the ones that don't know quite what they want so you don't have them upset after you're done, because even though they said they don't care what they get, they do now. Have them pick something, and go with that one. Let each person know you're on a tighter schedule than they are, but nicely. It's good you're not trying to figure this out last minute, but don't stress too much - my bet is that a lot of the girls will decide later on to get their hair professionaly done, no offense to you. It's just part of the prom experience. :) Good luck whatever happens!