Hi Heather
On the subject of what to wear, the key is to have lots of layers to hand. Because you are at high altitude for much of the trip, it can be hot when the sun is out then turn cold when cloudy. A t-shirt and a thick fleece is a good solution, as you can tie the jacket around your waist when it gets hot.
Humidity wasn't a factor on my visit. At this higher altitude the air is fairly thin and crisp, so I wouldn't worry at all about your camera.
For anything to do with jabs, I would urge you to talk to your GP's surgery or NHS Direct, as they will know much more about it. I think I had a yellow fever jab when I went, so that might be something to ask about. A good insect repellant is definitely a good idea (some sun creams include it).
You won't need to be superfit. No one on your trip will need to do any more walking than they are comfortable with, as we want everyone to enjoy themselves.
As for guidebooks, I like the Rough Guide and Lonely Planet, but have a look in your bookshop and see which ones appeal to you. For example, some have more pictures than others.
One thing to look out for is the painting of the Last Supper in Cuzco cathedral, featuring a guinea pig at the centre of the feast! The guinea pig is a delicacy here, and the painting is a fascinating example of the Spanish conquerors trying to make their catholic beliefs more acceptable to the locals.
Let me know if you have any more questions - Peru is one of my favourite countries!
Kind regards,
Olly, your editor