I'm trying to build my own responsive template.

I have a fresh install of zc155e. To that I added Clone a Template. After cloning Responsive Classic, I added then added the Responsive Color Changes mod.

I did read the documentation of the two mods above, as well as the CSS_read_me.txt, but I'm still feeling a bit confused. Forgive me if my questions are dumb!

First question:
Why can't I "Request Desktop Version" on my mobile devices? Is there something I need to enable in order to allow this? As a customer, I frequently make use of this on sites like Amazon, Facebook, etc, so I'd really like for my customers to be able to do the same if possible. If this cannot be done easily, I guess it's not a big deal.

Second question:
Which file controls the desktop version, explicitly? For instance, where do I set site width?

I know Stylesheet.css controls most everything basic. And I can change site width by altering line 99 of that file (Responsive Color Changes version):
/*bof wrappers - page or section containers*/
#mainWrapper {text-align:left;width:100%;vertical-align:top;}

But it also appears that I could change desktop width using responsive_default.css. What's the best way to do this?

Third question:
Hope this isn't painfully dumb, but what does "!important" mean/do? Like this:
.onerow-fluid{width:100% !important;}

And could I alter that as such:
.onerow-fluid{width:1200px !important;}

Last question (for now):
Is there a basic Q&A for the Responsive Classic Template out there, somewhere? And/or other general info writeups about building ZC and responsive templates?

Thanks!