Short answers, pulled from the story.
Emperor Ashoka of the Maurya Empire put up a pillar at Lumbini in the second century BCE. This event occurred after the Third Buddhist council when he sent missionaries to Nepal.
Shakyamuni Buddha was born in Lumbini within present-day Rupandehi District, Lumbini zone of Nepal around 563 BCE. The site holds profound significance as it marks where the historical figure entered the world before attaining enlightenment under the Bodhi Tree in Bodh Gaya.
The Licchavi period saw the flourishing of both Hinduism and Buddhism in Nepal from 400 to 750 CE. King Manadeva paid homage at both Hindu and Buddhist sites while religious tolerance and syncretism were stressed during this time.
Newar Buddhism is a form of Vajrayana influenced by Theravada Buddhism and is the oldest known form of the Vajrayana tradition significantly older than the Tibetan Buddhism practiced further north. The Paubha flourished during the Malla dynasty period between 1200 and 1769 as the Newar counterpart of the Tibetan Buddhist Thangka.
Theravada Buddhists were banished from Nepal in 1926 and 1944 for preaching Buddhism. A Sri Lankan goodwill mission visited Kathmandu in 1946 and interceded on behalf of the monks before the ban was lifted.
According to the 2021 census approximately 2.4 million people identify as adherents of Buddhism in Nepal representing 8.2% of the total population. Between 2001 and 2011 census the percentage of Buddhists declined by 1.7% from 10.74% to 9.04%.