I agree with gwovadis, 10 days is barely enough time to see Cusco and Arequipa highlights (I think Lima is worth at least 1 day to enjoy the country's best jewel shops and restaurants, food is unbelievably delicious, try Astrid&Gaston in Miraflores). If you have carefully planned your itinerary (with the help of expert fodorites) I don't think you will need travel agency services although I did request help from one of them (PeruInteract) to book Lan Peru flights for me and saved quite a lot even after paying a surcharge for credit card payment and service fee (it is not Apunake, I long found that just like Enjoy Peru this company is almost out of business and some travelers have had bad experiences with them lately). Immersion experience? Nope, you wont have time, perhaps submersion into one of La Calera Hot Springs pool in the Colca Valley is possible, but immersion as to close interact with locals for a few days, no. Just spend 1 night at Aguas Calientes and if you 2 in Colca (there are many more places to explore here).