The king's Speech has some great examples of flat frames that are visually interesting. Although not many are dead center. I do agree that the DP's job is to help you achieve your vision as a Director. If you want the shot try it. Otherwise who knows of it works. Mistakes helps us too, as long as we learn from them.
Speaking from a tech stand point I have seen well done 1080p footage from a DSLR outclass average work on a Red Epic. So for me a better color space, bit rate, and bit depth are more prized than the race for resolution.
On the artistic side the best thing I heard was from Janusz Kaminski. He said to watch life around you and see how light and shadows change and shift. That might be the best was to absorb without constantly creating content.
Check out this video from Film Riot:http://youtu.be/91sbBfTIHkc
They do use some After Effects work, but you can do it without the extra smoke effect that they add.
My suggestion would be find a used T2i, T3i, or Nikon starter camera (others will know more about Nikon than I). Saving money on the camera will give you room for better lenses. Good glass will always be a higher priority than the next best camera.
I would suggest, like everyone else, a 17-55mm or 17-50mm. Try and get something with a constant apeture like f/2.8, otherwise the long end of your zoom will get darker. Also if you can swing it get something that has Image Stabilization if you are doing any hand-held. As for crop factors don't get too hung up on them when looking at lenses.
If you are planning on adapting any old lenses check out this article.http://www.bobatkins.com/photography/eosfaq/manual_focus_EOS.html
It covers what lenses work best to adapt to Canon EF mount.