Our typical ratios are: 10 square meters per bed and one bathroom per 4 beds.
But then, space is not our biggest problem. Real estate is cheap in our cities - compared to NYC.
The hostel in Naples I´m staying at now has two bathrooms for 24 beds. One more would be really nice. And it sucks that the toilets are not separated from the showers. When people shower in the evening you always have to wait if you want to go to the toilet.
In NYC I would expect pretty crammed rooms as well. Bunks and lockers in the rooms, certainly no other furniture (like a table with some chairs) and not much space. If there are many people in a small room you´ll need some sort of ventilation and/or air condition, just a window won´t do, esp. if there´s a noisy street outside.
Make sure your common rooms are spacious enough and you´ll be fine.
Anyhow, I don´t think you can put more than 80-90 beds in a 500 sqm house or else it´ll be extremely crammed. If there are so many people in one little house it´s also a security issue, i.e. in case of a fire.