Poland / Open a hostel / Regulation

Hi there! I want to open a hostel in Krakow. But I have a couple of questions. Hope, somebody will help me.

1. What the main law regulation for hostels? Sanitary & Epidemiological Service rules, Fire Department rules, any licenses?

2. I found few options of properties but some of them have few rooms without windows. Question - can I use this spaces as private rooms for guests or it's forbidden by the polish laws?

Thanks!