We booked our tickets with our hotel. However I have seen many people selling in stores and on the street. I am sure that you could find a website where you could purchase online.
Well, there is nothing pornografic there. So safe from this perspective for underaged kids. But it is loud and they may not be interested in such form of entertainment.
Yes you can take photo during the show, but i suggest watch the show with your eyes and after show all the artist come outside you can take your photo with them with 80 Baht per photo.