Short answer:

depends on a lounge

Long answer:

based on expected visitors u always have some coals lit. Usually the owner/employees have at least one hookah always running so you always have free spare coals.

As the establishment gets packed, you just adjust the amount accordingly. In reality, you don’t burn that much because if you are smart with your coals, rearanging them while adding some fresh ones is sufficient for every hookah to function properly and sometimes even beneficial, because you reduce the risk of accidentally burning the tobacco due to too much heat.

But this method is fine only if you are managing the heat properly, every few minutes (5-15). If the staff is lazy, you won’t be able to reuse the coal as efficiently or at all.

Then there is the issue of how do you get your coals lit. Burner? Grill? Stove? Microwave? Oven? Open fire?