Since it is a duplicate and meant for mobile devices, then yes, I would use a canonical tag or even noindex if you don't want it in the index anyway.  Either method would eliminate the duplicate content problem.

Is the page with device=iphone&c=y different than example.html?  If not, you should make sure to add the canonical tag to it.  If it is different, then you shouldn't add it because it's not a duplicate.

I think the advice in that article is still relevant today.  Create a footer link to the "website credits" page, and give yourself a link from THAT page.

Yes, you can say CGI parameters = URL parameters.  I don't think many people refer to them as CGI parameters anymore though.

To answer your question, yes, as long as you have rel canonical set up correctly, then the URL parameters won't hurt your indexing.

For example, if you have your rel canonical set to http://mysite.com/japan.html

Then, only that page will be indexed, even if there are various parameters such as

http://mysite.com/japan.html?source=something&whateva=somethingelse

Just MAKE SURE to setup rel canonical correctly because it can be bad if you don't.  Check out Dr. Pete's post about this: http://www.seomoz.org/blog/catastrophic-canonicalization

The first question is why do you want to mask them? To hide the destination from search engines?  If that's the reason, it won't work, because they can easily follow your redirects.  If you're just doing it for URL vanity, then I don't think it would hurt, but maybe you should just transition the newer ones over time so you don't have a massive change all at once.

Do you get any value/conversions out of that type of image referral?

You don't need to worry about some sort of duplicate content penalty for using the same image/filename all over your site.  This is common practice, for example, Amazon uses the same logo image file on every page of their site.