multiple,camera

Hi~

I'm developing with Area targets AR App in ios, I want to know how can i add a function that users can take photo when they see the AR Object. Second, if I have three maps in three places, how can i let users can change maps in the App. Third, if I want to update the maps or the AR content in the maps, should i always change them in unity and let users download App again？Last, is there any requirement about 3D models in AR content, like size？