Buses from Kathmandu to Sundarijal leave from the Ratna Park Bus Station (Map Location: 27.705582, 85.314532) which is walking distance from Thamel.
The hike from Sundarijal to Chisapani starts out in Shivapuri National Park right outside of Sundarijal. Just go north on the only road and follow the big water pipe up the steps.
There are little shops and restaurants all along the way so water and snacks are no problem.
Most of this hike is uphill and much of the trail has steps. Once over the mountain there are some nice views of the verdant valley.
In Chisapani there are plenty of cheap hotels, some right at the entrance and some down the hill. They have nice views of the Lang Tang Himalayas. The best time to see them is right after sunrise.
This is a 'Teahouse Trek' which means that there are plenty of hotels and restaurants available so camping and cooking are not required.
These hikes can be combined to make a nice three day loop through the Kathmandu Valley:
Nepal Trek: Sundarijal to Chisapani
Nepal Trek: Chisapani to Nagarkot
Nepal Trek: Nagarkot to Naya Basti