I am trying to figure out if it is possible to go from Cusco to Puno and then return. I know there are buses and trains and flights(Juliaca). Is flying to Juliaca from Lima, staying for a few days, then flying to Cusco for a few days then flying to Lima feasible? Or are the flights unreliable? We are thinking of travel at the end of October and first week of November.
You can do as you are thinking, frlying from Lima to Juiaca first, visit Puno and surrounding areas, Lake Titicaca is a must-see place, after a couple of days you could come to Cusco, although, due to altitude sickness you may want to try coming to Cusco first and acclimatize in the Sacred Valley for a couple of days then go to Machu Picchu and on the way to Cusco visit the city for a day or two and just then fly to Juliaca, and sped a couple of days in Puno and finally fly to Lima.