I spent 6 weeks in southern chile in 2002 - the lake district and patagonia. 10 days were spent in Torres del Paine national park.
The whole park is spectacular, but there are some particularly oustanding features which should not be missed: the Torres del Paine themselves, the Grey Glaciar, and the Valle Frances.
There are two trekking routes, which take these sights in. The "circuit" which circumnavigates the whole Paine massif in take about 8 days, and requires a tent, and the "W" which covers the front side of the park, taking in most of the key sites in about 5 days and can be done entirely hut-to-hut.
I did the full circuit with a couple of side trips in 10 days, in a mixture of camping and huts. The size of your pack and the distances to be covered do limit your photography somewhat...i.e. no tripod and a limited selection of lenses to keep the weight down. I used an FM3A and three primes in a bum-bag worn in front, so I could access them easily.
If you take the "W" and stay in huts, you can carry more gear and take more time over your photography, as you only need to carry a day pack with lunch, water and a sleeping bag. The daily distances are similar, but as you are travelling light you go much faster. If you are planning this route, you need to book the huts in advance, especially in Dec, Jan or Feb. You can also book meals - dinner, breakfast and a packed lunch - at each.
The most common photographs you see in books are not actually taken from either of the routes, but from the southern edge of the park looking back over Lago Pehue or Lago Grey to the Cuernos del Paine mountains or the Grey glaciar. These are lovely views, but they are not nearly as spectacular as the ones you can get close up.
Are you planning on hiking/camping through the park at all, or will you be staying in one of the hotels and making day trips?
