Develop web app with Html5

I want to use HTML5 to develop a graphic design web app. Because of the limited understanding of this new technology and lots of HTML5-related technology and frameworks, I’d like to ask:

1. Is there any mature HTML5 graphics library for us to use?

2. How to modularize the core code to integrate it with other frameworks or transplant multi-platform? Any mature design ideas or practices?

3. Are there some mature cross-platform solutions that can easily support Android, iOS, windows and mac transplantation?

4. Any mature and useful recommendations for UI frameworks?

5. For developers who do not have H5 development experience, what is the suggested learning map?

Thanks for any suggestion！