Whatever you do in Kathmandu DO if possible take the morning site seeing flight along the Himalaya. There are at least 3 operators running the one hour trip ,starting from 07.00 hours at a cost of £100 ($170?) but they only run if the weather is good.
A takeoff at 08.00 in a Yeti Air BAe Jetstream 41 (17 seater) a magical flight along the range to Everest and including a flight deck photo opportunity. Great photos and great memories including the aircraft loading area with planes coming in every few minutes to pick up passengers for the next trip.
A Marshall's nightmare - 16 light aircraft,mixed in with buses and passengers but it all works.
DO it if you can!