Hi Loungepax, I go to Nepal very regularly and can give you some recommendations. If you don't mind having 5* accommodation you could stay at the Hyatt Regency in Kathmandu. It is close to an interesting area (Boudnath, with a very interesting Stupa and quite a few monasteries). It is a good hotel, with big rooms and a generator. Obviously you are spending time in a developing country so the contrast between your hotel and the city will be massive. The hotel is like a different world within the city of Kathmandu. It comes with a price, but compared to Hyatts in other countries great value for money.
However, the center of Kathmandu is a a bit out of the way. They Hyatt provides a shuttle service to the center though. You have to take a taxi back. Having said that - taxis in Nepal are cheap and if you are good in bargaining, you probably pay around 5$ for a trip from the center back to the Hyatt.
You can easily spend 4-5 days in Kathmandu. Pashupatinath temple is impressive. You can easilly spend a morning there to view the Hindu cremations and to walk around the temples.
Swayamboudnath is a great temple, on the top of a mountain with a great view over Kathmandu Valley. Lots of monkeys (avoid them) and you can walk up via the stairs from one site of the temple. Again a great experience to really experience the religion of the Nepalese. Take your time there. Arrive early in the morning, hopefully this will give you a clear view over the Valley and city. With a bit of luck you will have clear skies and you will be able to see the mountains.
Obviously Boudnath is impressive. Arrive around 4pm and walk around the stupa. It will get busier with Tibetan refugees walking around the stupa and the atmosphere is special. Have a drink or have some food at one of the roof top restaurants.
Spend 1 day walking through Thamel ("touristic center") a maze of small streets, shops, cheap buys and cheap guesthouses, hotels and restaurants. Walk from Thamel to Durbar Square (World Heritage Site) and enjoy the temples. Avoid the guides, they stick to you like glue. However if you want to support one of the "guides" make sure you are going to be clear about the price for their help/information. I always prefer walking around on my own.
A visa on arrival is easy to do. Fill in all the paper work before arrival. Bring a pass photo and 25U$. If you are quick getting out of the plane, your wait will not be so long.
In Thamel you can have nice dinner/lunch at the Third Eye of Road House cafe.
Don't forget to eat momo's (steamed Nepalese dim sums).
If you are not into hiking etc. you could always plan a mountain flight. It is quite amazing to see Mt. Everest from the plane. If you are going to plan this, do this at the start of your stay. If the weather is not good enough, they will cancel and you will be able to go the next day.
There is not a lot of 5* luxury in Kathmandu and therefore I think you can't go wrong with the Hyatt. I usually go cheaper and stay at the Ambassador Garden Home in Thamel. I like that place - it is clean - they are friendly and you are in the middle of Thamel and restaurants etc. are close.
If you want more information - or want me to be more specific - don't hesitate to ask. I have been going to Nepal since 2004 and spend approximately 4-8 weeks per year in Nepal.
I like the place, the people are friendly, but please remember: it is also dirty, noisy, chaotic and unpredictable.
I have more accommodation tips if needed.
Cheers
