I traveled Nepal from May 14 to the 24th, 2014. It was all arranged by Four Season Travel and Tours and I cannot imagine doing it without them. Nepal is not an easy trek even in the most developed parts.
Getting off the plane was a circus. First they claimed that that had no aisle chair. Then they wanted to charge me $75 for the lift-bed truck that they schlep you off in. There were tiedown slot in the floor but not straps or seatbelts! Nepal needs training by the experts at Open Doors Organization.