Re: big heads on celebrities
Apparently that is one of the things that attracts us to babies and children. Maybe it works for adults too

It works for my dog - he has the head of a 60-pound dog on a 20-pound body. And big ears
Re: contouring colors
I use Drama and Splendid, but anything 1-2 shades ligher/darker than your complexion works great. The lowlight should be matte and the highlight can be matte or shimmer.
Re: your photos
You are gorgeous!
Re: how to contour based on your photos (take this w/ a grain of salt, I'm a total amateur)
I have an almost opposite face shape to yours (small chin compared to my nose, when I'm feeling self-deprecating, I say that I have an 'alien head' - I also have these awesome protuberances on my forehead which only add to the 'alien head' effect), and I'm not a makeup artist so I am not 100% sure how to advise you on contouring. But, FWIW, here goes.
I would definitely say to place the light color on the bridge of your nose and top of your cheekbones. Your nose and cheeks are beautiful, and this will bring attention to your eyes and that area of the face.
Your forehead looks proportional to me so I'd leave that alone. If you want to narrow your forehead for any reason (like I do with my alien protuberances sometimes) you can place some of the dark color on each side to create shadowing, or, if you feel your forehead is too high, you can place some of the dark color along your hairline to shorten the forehead.
I would place lowlight on the sides of your jaw if you'd like to narrow it, at the corner of your jawbone, but BLEND THAT LIKE CRAZY. IDK what look you're trying to achieve but for mine I like to start under the cheek bone, sweep down the side of the face by the ear, go along the corner of the jaw, then blend it like crazy. This narrows the jaw and makes the face less square/round/heavy in that area.
I have no experience with contouring to de-emphasize a prominent chin... since my alien head requires the opposite... but I would assume that placing some of the lowlight on the places you would like to de-emphasize (like the tip of the chin) might achieve the desired effect. Let me know how it goes. Contouring takes some practice, at least it did for me. You can also place lowlight along the bottom of your jawline to help define it (this is what I do, it may not be necessary for you).
There are lots of these on YouTube, but here's a basic contouring vid:
http://www.youtube.com/watch?v=5Scq9vRzGc8
And another basic link:
http://www.the-cosmetics-campus.com/how ... -chin.html