+1 for weathersealing. Machu Picchu was extremely wet.. I went in January and it was a mixture of rain, cold, wind, then the random sun with nasty humidity. Street photography.. Cuzco was awesome for that. Puno, visit the floating islands. Besides that, not much to see/shoot. I would be careful with your equipment.. people don't care whether you have a nikon, canon, leica, hasselblad, sony, fuji, etc.. I didn't even use a strap. I shot then store away. Better safe! There are plenty of stories people being threatened with knives and stuff. Never saw and didn't happen to me. I spoke some spanish and also traveled with a few others at all times. Tip from locals, keep your bag in front of you. Worked for me and the locals. La Paz is awesome.. at night for photos. Visit some cafes and the city squares. Several of the cathedrals are nice. haha City is quite drab during the day. Dust dust dust is another thing.. It's pretty windy so I'd be a little cautious. Avoid the touristy areas if you want excellent opportunities for street photography/great deals.
I'd definitely take a wide lens!! That's the lens I used the most. Honestly, anything above 135mm, not needed imo. Maybe a prime lens? 50mm? for low light stuff/street photography. Spare batteries, cards.. should be good. Traveling light will make it more enjoyable. Have fun and share when you get back~