I think Baltic people = Dacians, proto-Slavic = north Thracians, Pannonians, Veneti, Scythians, and Scordisci/Serians/Serdi who are east Celtic people and spread along Danube...
so, a wild guess, why would -Esti not be related to Estonians?
"Bucu' in Estonian = "labour"
so, this would be...