I agree with bowman, your left side is bending more than your right side. That means you need to take some even scrapes off of the right side until it bends the same as the left. I know this doesn't sound helpful (I was in your shoes a couple years ago) but now that you have the bow bending don't worry about the thickness measurements, the only thing that matters now is the tiller. Take wood off where it looks stiff and leave it alone where it's bending too much. when the tiller looks good then you can take a little more wood off with a scraper and bend it a little further and repeat until you see another problem to fix. It's final thickness will be what ever it needs to be for your design, your draw weight, your draw length and your particular piece of wood. There's no way anyone can know what that's going to be. There are just too many variables.
As for how far you should be bending it, that will depend on the draw weight you are shooting for and how the tiller looks. You never want to pull a bow past it's intended draw weight. SO if you want a 50 lb. bow and it is pulling 50 lbs. at 13" then don't pull it past 13" until you taken more off. But more importantly you should only pull the bow far enough to see a problem with the tiller. If you see some thing uneven at 10" don't pull it to 13" until it looks even.