It's certainly possible to do this. Generally, I create a separate event sheet to govern my splash screen and all start up screens, instructions, level selector, leader boards, game over, etc... Depending on the type of game I try to minimize the number of event sheets for the levels themselves but, sometimes I create separate event sheet for each level. Really depends on your game but if performance is your concern, I wouldn't let that stop you from creating a separate event sheet. And sometimes it's best to create a separate event sheet for everything and then when your game is complete, migrate everything into a single sheet. You can separate their code into "Groups" that can be disabled when not in use for a particular layout.