If the URL works, you can test it before using it -- is the issue that the button is not doing anything or the the URL is wrong?
It's really your choice. If you use your document at http://www.houkenseido.jp/ as a starting point, it looks like you have created responsive layouts for different screen sizes. As long as you're happy with how it looks on different screen sizes, that's what matters 
This is likely your images 'preloading' before your scene appears. One way to speed this up is to turn off preloading for your larger images, or just preload a few key images that you want to make sure are loaded before your initial scene appears. This guide has a few tips on speeding up the initial load: Decreasing load times and optimizing performance: Preparing a Large project in Hype.
Excited to see what comes next!