Eastern Celts

Hullo
There are 2 main sources of info about Celtic life : the remains of buildings and forts, and written legends and records. These are limited and uncertain. So another scrap of input may be useful. Eire is at the far west and was undamaged by the Roman empire allowing old ways to continue to some extent. In the far east there seems also to be an undamaged remnant of the old ways.
Indo European culture spread from the Black sea - south Russia region so that rivers were named for Danu : Dneister, Dniepr, Don and Danube. Danann and Boann of the Boyne may be part of this. Legends of cattle being seized and a hero / snake ancestor-legend are associated with these. Connal Cernach of Ulster and Lombardy is an example and the source of the Danube has a dragon myth , like Danu and Indra in the Vedas.
From the Mari , Hurrian and Persian horse-tribes there was a movement south to India , taking Indo European languages such as Persian dialects and Sanskrit. Persian Kambojas who had been south of the Caucasus traded "kamboja" horses to Sri Lanka from about 2300 years ago.
From there Indian traders sailed to Asia from that time and developed Hindu /Buddhist kingdoms. Today there are remnants of a rigid lord-client culture like the Celtic structure of Eire in the island of Bali Indonesia. The last ruling king was murdered by Dutch in 1906. But the sacred pools and Brahmin leaders exist in ritual and an orderly spiritual society having the goddess Danu at beautiful temples near her lakes.
So it may be that early times in Eire can be visualised by comparable life in Bali