Giving expenses of compensations from the zakah is unlawful. A madrasa should employ such people who collect donations and should give their salary from other funds like imdad, atiya etc.
(2) Once a land is endowed as mosque and people start offering salah there, it becomes mosque from beneath the earth to the sky. The place allotted for salah is called masjid sharyi and the rest carry the ruling of waqf, the part of masjid sharyi will carry exclusive rulings of masjid sharyi. As far a place which is not endowed, only salah is offered there whether five time regular prayers or Jumuah, it will not be considered masjid sharyi. By praying salah there, one will get the reward of Jamaat, but not that of mosque. Therefore by praying salah with Jamaat in lower floor people will get reward of salah with Jamaat, but not that of mosque. It will not carry the ruling of masjid sharyi.
(3) If the owner has endowed it, or it was bought by the income of waqf, then it will be considered waqf.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband