You could take a flight from Dushanbe to Khorog. There is a 14 seater flight every morning to Khorog, but its departure depends on weather conditions and the number of passengers. Tickets to the flight are sold a day in advance at the Dushanbe airport.
You could share/hire a jeep from the jeep stand near the airport in Dushanbe to Khorog. This will take between 13 and 21 hours and privately hiring a jeep costs around $400.
From Khorog you can hitch on a fuel tanker or truck on its way back to Kyrgyzstan, or hire your own vehicle from Khorog. Its also possible to get an occasional shared van to Murghab and from there to Osh. Most days will also see a jeep or share taxi head towards Ishkashim. Hitchiking on the Pamir highway requires patience. The first vehicle with space will give you a ride, but as with many places in the former Soviet Union you are expected to pay for the ride. It can take anywhere from 2 hours to 2 days to get a ride. There many only be 2 or 3 vehicles going in your direction each day.
Same as getting in.
Rice, eggs, snacks, yak butter, bread, mutton, Pamiri tea (sheer-chai), freshly made warm bread (non).
Tea, surprisingly good coffee, and vodka. Yak milk.
There are a number of homestays in most villages on the Pamir highway. They are usually in homes built in traditional Pamiri style. They are made with wood, with five pillars, a sky light and richly decorated with carpets. You are ensured great hospitality and simple but delicious meals.
A zealous policeman in Murghab may want to register you with the police or complain if you were taking photos. This isn't a problem, registration should be known well enough simply getting to the area.
There is some risk of altitude sickness.