If you want eggs, I've heard the ratio is about 3 quail eggs is equivalent to 1 chicken egg (but adjust accordingly if you have another ratio that you agree with more). So depending on how many chicken eggs you might like to be eating on a daily or weekly basis, calculate that for the estimated number of quail females you'll want, and then the general ratio of 1 male to 3 or 4 females will then give you how many males you'll need. That number then gives you the amount of space and feed you'll need, etc.
As for the eggs to hatch out, I usually expect about a 50-80% hatch rate, and then maybe after that, another 5-10% might die as babies, in my experience. This includes they get trampled on by the others for sheer numbers, or they can't get food/water as often as they need before you noticed they are too weak (and get trampled on). Other times they may develop mobility problems (splayed legs, eg) and you may not want to keep them around to adult hood since they'll depend on you pretty much for their care.
However, this number doesn't need to be too much of a worry if you are producing eggs regularly. In other words, even while you have one batch of eggs in the incubator, you are constantly getting more eggs, and over a short period of time, you will have plenty of eggs to eat, hatch, or count as losses after they hatch.