Good work, but I do detect some minor inconsistencies.

They were formed after 278 BC, as some of the survivors of the Celtic invasions of Greece settled the abovementioned region imposing themselves as a thin, yet powerful, ruling class.

The tribes of Autariatae and the Celtic Scordisci are thought to have merged into one in the Lower Morava valley, Serbia, after 313 BC[.]
Which seems to imply that they arrived after merging with local tribes and leaving burials in the area?