You need to advise public authorities: i.e. if in the same place there is another event and the two groups which may not like each other meet ( for example fans of rival teams) ...things will go bad. Or simply authorities have to alert medical cars to be on standby ( Look at any concert of any musical group) etc

You need to have license to hold the event, the place may no be' big enough or safety exit could be' missing ( huge crowds can create hundreds of death , see in south korea this year) .

Also, you are none to tell the owner of a property that he is "wasting" that building... so what? If another comes telling your music is garbage and there should be' another event, who win? Are you going to do a war about it? Simply your logic is not how private property law works anywhere in the world.

Last of things, pay royalties for the music. But I am not going to argue of this last point as it should be the support you give to the music you love and anyway is really the minus of all the priorities.

Yes, we majority of italian people do not want you and friend to party in my private property and create a mess. If you want to make a public event you will have to get license ( about place safety plan, music license etc and permission of the property owner). It is democracy , respect it.