Arrange a party, things to think about

Hi!
Im writing in english because my keybord is not swe/layouted...

Well me and a few friends are gonna arrange a party, at a public place.
Its a concert like party, so were gonna have a stage and sound system.

Were thinking we need
soundsystem
stage

its not a closed party and no entrance fee, will this affect anything?
its in a park.

well what do we need, permission with the authorities of course.
Is security or something necessary?

ye well what do you know?

Shamzi