So, basically, you want someone to teach you everythign there is to know about writing a custom control??
That's just not going ot happen in a forum environment. The amount of knowledge required is WAY TOO MUCH for a few forum posts.
You can start with this
You better put this project on hold until you learn how to make custom controls first. Then you'll have to apply that knowledge to designing your control. Really, a stack panel is just a Controls collection that controls the positioning of the controls in its collection.
You're going to have a big problem though. Since controls in Windows Forms don't behave the same way the equivilent control in WPF do, don't expect to come up with the exact same behavior as the WPF StackPanel. You'd have to create an entire family of controls to duplicate that. But then, why would you when you can save yourself all of the work and just use WPF??