Besides the ceremony which if it is called a coronation in English even if it will be more a blessing with sacred water than an actual coronation, there will be several parades ibn Bangkok. A dedicated webpage was created by the authorities about the event for those who would like to know more about the rites of this event, just have a look here. Note that several roads in Bangkok will be closed on those days and Grand Palace and Emerald Buddha Temple (Wat Phra Kaew) will probably be closed to visitors at least on may 4th.
More information : https://thailand.prd.go.th/ewt_news.php?nid=7716
With a lot of traditions, festivals in Thailand are numerous and some are worldwide famous. Loy Krathong sometimes also called the Festival of Lights is held in November and was elected second best festival in the world. It must be said that this is the most photogenic festival in Thailand.
The main events of the Buddhist calendar but also the anniversaries of the King and Queen of Thailand and other days related to the History of the country are holidays in Thailand. If banks and administrations are generally closed those days, transport, shops and restaurants operate normally.