Take a warm sleeping bag & plenty of warm clothes - it was really cold at night (we went in late Nov / December) - we slept with the toothpaste in our sleeping bags so it wasn't frozen in the morning. It also helped to keep the camera in the sleeping bag overnight to help save the battery! But it was a really good time to go despite the cold as the weather was spectacular and the lodges were not so busy.
Take a good water bottle - you don't need to buy bottled water on the trek - it's a lot cheaper to buy boiled water - but it is hot when you get it! I had a platypus but the hose kept freezing up during the high days. The food was really good - lots of great soups.
I didn't find the walking too difficult - and I'm normally always well out the back. Nice relaxed pace the first few days, plenty of long stops for tea and lunch. Then further up it gets harder as the altitude kicks in, but just go really slow and you get there in the end!
Drink loads during the day (plenty of opportunities to stop for pots of lemon tea) but go easy on the fluids in the evening - there is no way you are going to want to get out of your warm sleeping bag in the night & visit the toilet with the floor covered in ice!
Take plenty of strepsils & tissues with you - altitude & the dust make you really snotty!