That's the topic covered here by Mark Barnard, associate head coach at Oregon State and the head coach of the Australian women's national team. He outlines several criteria for judging how much offense your players will be able to handle, and he also emphasizes the importance of having your team master the 1, 4 and 5 sets before trying to get fancy. In his view, predictable is OK as long as it's well executed.
Before you determine how complex your offense should be, you first have to take an objective look at your players. If a lot of them aren't yet sound in the fundamentals, running a complex offense will likely do you more harm than good.