You do sound like you have a solid position here for primary custody. You are already doing all the primary parenting stuff, and have a flexible schedule that lets you do so, while your wife has unpredictable hours. Take a look at this list of factors my state uses to determine who the primary caregiver is. See how many apply to you, and think about which ones your wife wouldn't know:
http://www.dadsdivorce.com/father_divorce_forum/viewtopic.php?f=4&t=39880&hilit=primary+questionsI agree with Hoosier Dad above, and would even take it a step further, personally. Your wife thinks she'll just be able to walk into the court room and tell the judge her story, and get custody. Think strategically- use this to your advantage! Do not hint that she's in for a fight, and in fact, even drop subtle hints to her that you think she's right, and that you're at her mercy. That's what I did, and it worked out well in my case. My ex felt so confident, that she didn't prepare. She felt confident enough to do whatever she wanted- spending more time with Mr. Wonderful, partying, working, NOT taking care of our daughter, and so she never bothered to really study the law and learn how much these things were hurting her case. She didn't bother really strategizing with her lawyer. Meanwhile, I did everthing to improve my position and
document it, while letting her think I was a whipped puppy. When we got to the courthouse and her lawyer saw my foot-thick stack of evidence, and learned the real story, she folded. She conceded primary custody to me without a trial.
You have a golden opportunity here- it's great that you found this site now. Learn all you can, document, strategize, let your wife live in her fantasy land, consult lawyers, and learn the factors your state ususes to determine custody, and keep all this absolutely hidden from your wife.