I would say one sex act for every chapter would balance it! 8D Like if your roleplay was organized scene by scene for the chapters. Say today's scene was about the events at a party, aaall of the juicy party drama between blahblah characters, and then a sex scene in a closet. Or if the scene was about something shitty that happened at school, and then makeup sex in the car.
"Balance" is prolly going to mean something different for everyone. O__O I know that for ME, I can't just have two characters show up and start having sex, and then keeping doing random sex scenarios. I like to build relationships between characters, and create a story about those people and the world around them. Then all those sex scenes in random places are soooo much more interesting for me!