Possible, but considering JS hogs too much browser resources makes it not recommendable. Especially when the apps are big and the client has low memory. Though WebAssembly might address this issue.

I am not really sure if Ruby is the trendsetter considering "Convention over Configuration" but there are other frameworks, not only PHP, that is taking advantage of this -- consider Ember.js for instance.

Just do the #1 from the list of @Kleo then start over n times until your 24 hours is depleted.

If you are looking for CSS properties or HTML5 elements supported on different types of mobile devices, you may find this site useful: http://caniuse.com/#comparison Try it before actual testing features on an emulator.

They used Ruby on Rails on NginX.

For simple requirements, I would recommend Linode or DigitalOcean. Both gives total control of your box and requires system administration skills. If your concern is scalability, I would go for Amazon Web Services. But aside from system administration skills, it will require you to learn AWS interface and/or console thus with the learning curve. But if you master how AWS works, scalability won't be an issue anymore.

Wait and see this 2015 as I suspect that PHP will make it on top due to the combination of PHP 5.4+, Taylor Otwell (Laravel) and Jeffrey Way (Laracasts).

Yes, exactly my dilemma. Technology is promoting RWD but we cannot deny the fact that most projects require different content and layout across viewports. Another thing to consider is cost implication. RWD is economical compared to multiple versions that cost more time.