There are only three male roles in Hollywood Lies - but unfortunately it's not really possible to change their sex. You're better off choosing some of your brighter kids to dress up as men - we know of other all-girl parties where that has worked well.
As for reducing the number of characters, I would drop the following:
* Brian d'Lessey
* Les Tytan
* Ghana Moon
But please note that if you do drop these, some of the plots may be a little lopsided - if you possibly can, I recommend finding an extra three people!
I hope that's helped,