Have you checked out the Windows Store apps Dev Center lately?
It’s been filled with excellent resources for learning about and developing Windows Store apps. From code, to design guidelines, it’s chuck full of what you need to develop Windows Store Apps.
Feature guide
Product guide
Getting started
Support forums
Design downloads
Our design principles
Index UX guidelines
iPad to Windows Store app
iOS
Android
Windows 8
WPF/Silverlight
Samples
API reference
Downloads
Certification requirements