Can we see the score we can have before begin the song?
I perfect the song but i can't clear the event beacause i haven't enough score and i don't know before if i can reach the score.
Well, yes it is possible to calculate the maximum possible score, with small deviations due to rounding and stuff. But it would probably take more time to make this calculation (since it depends on a lot of factors like the costume, accessories, idols and their stats, song and the event itself) than just trying to do the event.
If you are interested in an in depths analysis of the scoring system, as well as some tips on how to improve your score, i posted a guide on GameFAQs:http://www.gamefaqs.com/ps4/730583-the-idolmster-platinum-stars/faqs/74300
With the information there you should theoretically be able to calculate how many points you are able to make with your current setup.