I may make the switch to a Mac, a few questions though

So, my Asus ultrabook i bought two years ago is having some issues, and it may be time for a new laptop, and this time i have the MacBook Air on my mind (dat battery life).

But I have a few questions regarding the switch:

1. Full screen apps, in Windows, im used to the simple fullscreen button, but in my understanding for a mac, this is program-dependent? The developers have to code the ability into the app for the fullscreen? to be possible And how does this fullscreen work, I've been told by a friend its similar to iOS fullscreen, as in it shuts everything else out of the window. What this really reminds me of then, is metro apps in Windows 8 (which I am not a fan of tbh). Anyways if you could shed some light on that, it would be appreciated.

2.OS X Mavericks. If I buy a Mac now, will I get a free upgrade to Mavericks? If you bought a Windows laptop after 8 was announced, it was a free upgrade, which makes complete sense imo. Or will I be buying the Mac now, and Apple expecting me to shell out $40 for the upgrade 2 months from now?

3. Dual-booting Windows. Yes, I know, I've brought up Windows multiple times. I will still need Windows as I need to test IE. Is it preferable to dual-boot Windows, or to use Parallels or Bootcamp? Is it a hassle dual-booting Windows (does everything work properly?)

That's all I can think of right now that has had me a little nervous about the switch. :)